Flash Heal v Binding Heal
It is my humble opinion that Flash Heal (FH) has now gone the way of Prayer of Healing (PoH) in becoming a main stay M+ heal and only used situationaly in Raid healing. Ok, so lets do the math...
Flash heal /475% sp + Echo of Light /185% sp = 650% sp with 1.2 sec cast
Binding Heal /300% sp + Echo of Light /117% sp = 417% sp with 1.2 sec cast X 3 = 1251% sp
That means for every flash heal at 650% sp you can cast a Binding heal for 1251% sp over the same cast time. Even if you take the Trail of Light talent you only add 260% sp to make a total of 920% sp. So without the ToL Talent (Never take this) your BH is almost twice as powerful as your FH.
I have heard the argument that you want to put all your sp into that one target with a flash heal to get them up asap, but is it really worth it when a FH gives them 650% sp and they get 417% from BH? 64% of the input (single target) from 60% of the mana a Flash Heal costs.
So all that math makes the brain hurt but there is a certain sanity in my theory... Because of the mana cost of the Bh you can cast almost twice as often as a FH while getting twice as much output per cast... wow, twice the output twice as often? yeps. So although the FH concentrates a little more output on a single target the BH is beter for raid wide healing keeping more people topped more often. In reality you don't always need to cast twice as much BH as FH so the mana saving is enormous, and this gives you so much opportunity to LET RIP. You have the capability to constantly and consistantly cast BH as a filler without ever running out of Mana. It is a smart heal so it will always target those that need the heal. You could argue that what if YOU don't need the heal, well in that case you are still healing two people and out performing a FH anyway. The reality is you can put yourself in positions that you would not normally and accept more damage knowing you are covered.
No need to take the enlightenment talent because Mana isn't an issue anymore (you should always use leytorrent potion anyways), no need to take the Trail of Light becaue you rarely Flash heal so that leaves you with what i consider the ONLY choice and without doubt the strongest- Enduring Renewal. Binding heal will refresh the renew on YOU, your TARGET and the REFLECTIVE player as well. 3 renew refreshes in one cast. Of course you very rarely cast renew as a hard spell, it all comes from your Prayer of Mending (PoM). Precast it on yourself before the pull and it will stay there the whole fight. Because you take the Binding heal talent you don't take Piety. oh boy! the Piety build. It sounds so awesome - all that serendipity making sanctify available so often,,, but, I have run with many priests with this build and never, not once has this build beaten the Binding heal build for out put. NOT ONCE. i have given my thoughts to others and they have switched and never looked back. We are talking a 25 to 40% increase in output just by switching to BH build. Sanctify is still available to the BH build just not so often - but ask yourself, Do i need to use it that often, spend that mana so often and be FORCED to use Flash Heal and even worse... cast Heal because of mana concerns rather than because it's all i need to use. I found myself answering NO to all of the above.
BH refreshing renew on 3 players at once (if they have it), Benediction giving the renews through PoM. As you go deeper into the fight most of your raid has renew on them and you find yourself chasing the renew timer with binding heal. 30% of your healing coming from a pell you didn't even cast. In my opinion just as much fun as chasing those Atonement procs in disc. All this goes to making Binding Heal the most essential spell we have as a holy priest, a huge amount of fun and no healer gear for gear will be anywhere near your figures. Not even Disc.