First of all, what exactly I mean by positioning is that of course your rotation will affect your dps, and we all know the optimal dummy rotation based on our gear/buffs. However, your rotation is actually dynamic. The correct rotation can be directly dependent on where you are, if you are in special situations, jump back to your regular rotation, then switch again, though this seems to be more present in heroics chain pulls than in raids (where DS priority can increase). In raids, the most important positioning is that of having a maximum dps uptime on the appropriate target. A simple version of this is Algalon, where you can avoid the main cosmic smash damage even if the tank does not move Algalon while staying within melee range.
On my server, there are lots and lots of rets who are better geared than me since I haven't raided consistently in a long time, but at the same time their dps fails. Certainly many of them use the wrong FCFS rotation, or else they don't faceroll hard enough, as is evident from recount parses. However, many others I have observed suffering huge dps differences between, say, hitting a single target nonmoving target, or participating in encounters that require movement.
Consider Twin Valkyrs. This is an example of maximizing dps uptime while getting ecounter buffs. Most pugs on the server tank the twins together in the middle of the room, in cleave range, rather than at the door. Now at this position, there are a few options. The first one, which many pugs do, is simply stand there behind the twins and not move all encounter long unless they need to switch colors, or if there is a massive amount of opposing colored balls about to hit their location. Another option is to chase balls around the room, pew pewing when there is nothing else in sight, until you get Super Saiyan'd, and then repeating until the twins are dead. The former is just bad, and the latter is not reliable as you lose dps time, and as the distribution of balls is random, it is not a good rule to follow.
Another possibility is to try always to remain in melee range, and adopt a fluid ball chasing strategy. Note that if you are doing HM, you will probably be clustered at the door, so this does not apply quite as heavily. The twins don't have a particularly large melee range, but it is sufficiently large that you can move around a nontrivial bit and still be able to hit them. Therefore, the easiest balls to grab are those that you can grab without leaving melee range. However, the balls also have a bit of splash, so you can actually pick up orbs that are out of melee range without leaving melee range, so long as you see someone else about to pick it up, and you can get within splash range of them. Of course, it is permissible at times to leave melee range, especially if you can go out, get an orb, and then come back all within a cooldown period. Yu may actually be able to time it sometimes, so that you run out in between melee swings, if by chance this is not happening during the time periods where everything is on cooldown. This is doable, though rarely, if you use the splash range, though usually you will have to suffer the loss of just over one GCD doing this unless you are lucky. Also, if you see a particularly large cluster of balls, then time it so you can run there, get buffed, and come back in the least possible time. You should NOT just go and chase after them from the get go.
Remember that on Valkyrs, chances are you will only get the dps buff once throughout the entire encounter (unless you are both good and the rest of the raid dps bad). You will also most likely get the buff and have it end before the fight ends. Therefore, you do not need to take too much special attention to getting the buff, though generally you should try to get it just before a special is cast, since having a buff which coincides with a special uptime has a chance of causing a dps uptime loss.
The latter strategy is what I used on valkyrs when I returned to raiding during winter break, and it was good for #16 US on WMO in my rather bad gear (no DC of any sort, using greatness and wrathstone, and a few ulduar 226 gear), though my gear has improved a bit since.
Another example of the above type of positioning mechanic is Hodir hardmode, as even the slightest dps uptime loss can (especially back during the period just after release) be the difference between a successful kill and a fail.
There are other somewhat more subtle positioning mechanics that you can use to your advantage as well. We'll cause this an example of maximizing dps uptime while avoiding death mechanics. Consider Firefighter. Suppose a water bomb is nearby, but not too near. Often, you can max melee range Mimiron in phase 2 in order to avoid a water bomb. Sometimes, you cannot. In these cases, you can time your exiting melee range so that you exit, avoid the water bomb just in time (plus some buffer, because lag can happen), and go right back in, without going too far out. This is similar to the ranged positioning mechanic on Vezax hardmode. However, most melee I observe go excessively far out, or stay out longer than needed. Also, consider the shock blast. You don't need to run out excessively early, or go very far (the range on it is actually pretty low). Then there is the spinning up in p4, which is usually adjacent to shock blast. All you need to do is position yourself run to the side opposite of the spinning up rotation, which sometimes involves running through Mimiron, and you will be safe. You don't have to actively run with Mimiron really, as doing that increases the chances of you reducing the uptime on your castable spells through multitasking error.
That last point is the central point of all this. Every decent paladin knows what a stationary dummy rotation is, and given equivalent gear and latency, they would probably all be within simulation error of each other. However, what many (especially new) paladins don't seem to understand is that the next most important mechanics in actual encounters are
1) Move as little as possible
2) Premeditate your strategy so that you need to multitask as little as possible
Combined, these two form what I consider to be positioning mechanics. Therefore, I think when people ask for help on their dps or theorycraft, the encounter should also be mentioned. Although certainly many encounter mechanics are random, there are certainly specific relative timings (if not some absolute timings in some encounters) for certain exact actions, all within a specific raid strategy. Thus far I don't see much telling a new paladin seeing Yogg for the first time what exactly to do, to maximize dps uptime throughout all phases of Yogg. There is just the general raid strategy which one can find in many places, but nothing specific. It's just like the difference between stating "you do a +1 zealot and archon rush out of 4 gateways" (which seems to be the standard type of advice) and
* Standard FE opening up to nexus initiation.
* 18 - Gateway (At the latest, should go up immediately after your Nexus)
* 20 - Main Gas
* 22 - Cybernetics Core
* 25/26 - Natural Gas (Must go up before the Core finishes)
* Optional - Dragoon (To chase off/kill the Zerg's Overlord in your base)
* 100% Core - Stargate
* Next 100 Gas - Citadel of Adun
* Next 100 Gas - Corsair
* Next 100 Gas - +1 Attack
* Next 150 Gas - Templar Archives
* Add 3 Gateways
* 2 Archons (Merge from 4 Gateways)
* Zealot Leg Speed
* Pure Zealots until +1 is almost finished, at which point you move out.
To use a Starcraft analogy. It's things like the latter that I believe would be more helpful to newbies
I'll write some encounter specific ret timing guides if there are any specific requests, but I anticipate that each guide would be rather time consuming to get just right, so therefore I'm not going to immediately try to write a detailed guide on every encounter in the game from the ret perspective.