This is the best I could do. I do apologize that I take on the stance of explaining why clicking is bad. I don't mean to tell anyone specifically they're wrong or call anyone out, only to try to explain this the best I can for OP and anyone who may care. I'll attempt to contribute to the thread by offering rebuttals to poorly constructed reasoning. Many arguments given either way have been full of error. I will refrain from using names because I do -not- wish to be insulting. I'll be around to continue to answer questions or respond.
The Short: Keybinding overall is a performance increase. Clicking requires less work to learn.
Arguments that aren't valid:
Statement:I click and I regularly beat key-binders I play with:
Answer: Personal evidence is anecdotal, meaning, it's a small sample size. This doesn't factor in the skill level of the players you're playing against. As a feral druid I regularly out damage many players of many classes. The fact that I outdamage most mages I play against does not mean mages do less damage than feral druids. It means they're worse players than I.
Statement: I only have to move my mouse as fast as the global cooldown, as long as I click the ability by then, I'm doing the same damage.
Answer: This is a horribly false statement made by many who don't understand the mechanics of cast bars and latency. You're effectively reacting to a finished cast and waiting to see the GCD pop so you can click. What this means is the time difference between the global cooldown coming up and the next ability going off is effectively going to be the following. Your reaction time to seeing the GCD come up, plus your latency. Players who keybind and maximize damage will spam their next damage effectively eliminating reaction time to the global cooldown and only dealing with latency. Human reaction time is larger than many people wish to admit.
In addition, many abilities do not incur a global cooldown. The way to get the highest damage is "Cooldown Stacking", meaning, to layer as many of your cooldowns on top of each other as you can. During heroism you'll want to use a potion of your stat choice and as many cd's as possible. Clicking requires hitting each of these and wasting time moving from one to the other, meaning you're wasting time that could be overlapping cds.
Statement: I can use macros to stack cooldowns for me.
Answer: This is true! I commend you on your use of macros to add benefit to your game play! The major issue with this however is that the vast majority of your cooldowns do not have the same cool down time. For heroism or bloodlust, you'll want to stack as many cooldowns as you can. The issue is, that often means using some abilities that have 45second cds, 3minute cds, 5 minute cds.. all sorts of varied time, on top of each other. As a result of stacking cds being the most damage, it means I want to stack them as often as I can, while using abilities as often as I can. I may wish to save my five minute cd, knowing I'll only get to use it once a fight, and want to use it for heroism. That may not hold true with my other cds. I can use them many times and still have them to stack when needed, if I time it well. For a clicker, this means having many buttons on screen. This eats both screen estate and movement time of the mouse.
Statement: A custom UI can facilitate clicking and let you do just as well as a keybinder.
Answer: No, it won't. While I will fully admit muscle memory can help you on your clicking crusade, and you may not have to look at your icons -as much-, you still will look. The reason you'll see top players use add-ons that move the important information near the center of their screen is a simple one, it allows them to get vital information quickly without having to look away from the center of their screen. This allows them to see their character, the fight, fight mechanics, their raid. You could move the abilities you click into close to a circle around your character to try to facilitate clicking... but doing so means you've added things to spaces that could show you other things. Important procs, debuffs, ability timers. All classes have buffs and debuffs they monitor, procs, things they watch. The faster you react to these, the more damage you can do. Moving them into your peripheral vision often means it being harder to register when you need to react to them.
Statement: I'm a healer in PvE, I do the same no matter what.
Answer: Nope! I'll -more than agree- that the issue becomes much less exacerbated as a PvE healer than any other roll. As a main spec healer I can in fact sympathize with the argument that clicking and mouseover healing pose much of the same problems. You'd be absolutely right in saying that you can configure Vuh-Do, Healbot, Grid or Xperl to do a lot of nifty things. I'll answer mouse overs right after this. Before that, I will say that using any unit frame, clicking a target, then clicking an ability and then clicking a new target is beyond slow. It's horrible. You're wasting time multiple times inbetween casts.
Mouseover macros thought addons such as Clique.. or binding abilties -to your mouse- once more means you can only be pressing one thing at a time. If you want to hit things the quickest you physically can, you should be using your q,e,r,t,f,g,z,x,c keys to bind healing cooldowns and utility abilities as well as some healing abilities. When I'm on the move, I often want to use my mouse to turn, my wasd keys to move, and then, if not for other keys, I would have no way to heal. To this regard I use my F1, F2, F3, F4 keys to target the tanks or healers, and my keys to cast instant cast abilities. In this regard, you're removing options you have to pull small inches of performance you could otherwise have.
Statement: There are gladiators that click! I've seen them!
Answer: I've also seen gladiators with missing fingers, missing arms, and in once case.. one that used a pencil to push keys to break 1800.
These things are by no means optimal. I'm not going to hold my arm behind my back to accomplish the things they did. The fact of the mater is, they are a small minority. They are -not- an exception to the rule, they're simply exceptional clickers. I -shutter- when I think about what these players would be able to do if they had the ability, know how, or limbs, to do things optimally. This is not a case of clicking being better than keybinding, or even vise versa, this is a case of those players having more skill at the game than other players. As said before, given -equal skill, gear and luck- keybinding will do better.
Statement: I'm not a world top player, it doesn't matter what I do! It's the same.
Answer: Well, I do certainly care less about which you do. It's less likely to matter which you do, but you could always increase your performance. By those standards, you aren't a top raider, you dont need to use your cooldowns because it wont matter if you do more damage or not.
-It may not make or break raids, but it IS a performance increase.-
Statement: I'm very agile! I can heal through clicking.
Answer: You're healing through mouseover macros, you aren't clicking your abilities on the screen. If you were, that would require clicking someone to target them, clicking the ability, and moving on to the next person and ability. You're using, gasp, mouse bindings. They are the same thing as keybindings, except, you know, on your mouse. They offer all of the shiny things keybinding does, and none of the horrible things that clicking your abilities does. It's an extension of keybinding. You're using unit frames, your keyboard and your mouse. You arent clicking things. If you are, you're likely clicking large cooldowns, which would be better put on your mouse or your keyboard.
Statement: Mouseover macros are CLICKING ABILITIES.
Answer: Flawed. You're confusing the concept of mouse binding with clicking. You're binding abilities to something so that you don't have to physically click the heal or ability icon on your screen to cast it. That's binding. Open Clique, it's called "Clique Bindings." Open Vuh-do, it's called Vuh-do's bindings.
Statement: I can make macros for that. Target of Target macros, last target macros, and so forth.
Answer: You're once again cluttering your screen estate. I can use my mouse to click a nameplate, hit an ability without having to move my mouse, and move back. I can make macros that are target=mouseover, mouseover a target, hit the ability on my keyboard, and move on. I will have SO many less icons than someone trying to play on a similar level. The amount a clicking player needs to play on the same level as a keybinding one is large and continues to take more attention and time.
Statement: "Occam's Razor means-other things being equal, a simpler explanation is better than a more complex one-."
Answer: That, like many other things, isn't correct. In practice, the application of the principle often shifts the burden of proof in a discussion. The razor states that one should proceed to simpler theories until simplicity can be traded for greater explanatory power. In this case, the ability to manage your abilities in multiple ways, using things strung together in multiple ways by having multiple buttons would be the greater power.
Statement: "You can hit wrong buttons when you keybind, what happens when you HoP the tank?"
Answer: You can accidently click the wrong thing too. If you're taking the time to visually look at your screen to be reminded of where buttons are, you're taking the time to stop casting or look away from things like fire, mechanics, your own characters procs. With practice comes muscle memory. With time comes memorization. For all things. The fact someone can argue they never miss a button clicking simply means they're practiced in it. The same applies to keybinds, a visual reminder isn't needed. I would tell you that I don't miss my druids abilities, but that's anecdotal.
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Pro's and Cons!
Clicking-Using your mouse to click abilities shown on as icons on your screen.
Pros:
-It's friendly to players who play the game socially. There is no time investment required to just start playing the game.
-Little to no learning curve.
Cons:
-Makes movement while dpsing hard.
-Makes targeting while dpsing harder than otherwise.
-Time moving mouse from ability to ability is time you could be doing things.
-Screen real estate, binding means being able to hide abilities meaning less clutter on screen
-Turning with keyboard while clicking abilities is infinitely slower than the reverse
-Requires looking at abilities rather than boss fights.
Keybinds
Quite literally take the opposite of what I posted for clicking.
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Supplements: Things made to help players.
If you'd like to improve your dps, a short video by Kripparrian is always a great place to start.
http://www.youtube.com/watch?v=VgDjG_0ecTI
If you'd like to -learn- how to keybind, an out of date post by myself in the rare guides section!
http://www.mmo-champion.com/threads/...How-To-Keybind
Note to Mods: I do apologize if this was too long, or anything of the sort. I was going to make this longer, and explain the points of why keybinding was helpful but realized this was getting far too long.
Final note to players:
Clicking is sub-optimal. That doesn't mean players who do it are bad. There is a difference in the words. You -can- be a good player and a good clicker, but you'll never be -as good as you could be- like that. That's all.