On Prayer of Healing

I've been looking at Holy specs as my guild is sorely lacking raid healers at the moment. I was holy throughout classic and tbc, and I keep up to date on the Holy spec even though I don't play it, so when a guildie asked about Prayer of Healing, I felt reasonably comfortable with answering. The question was about Prayer of Healing, and whether a certain Holy priest was playing badly by not using it more. So the question was: Isn't PoH one of the main tools in a Holy priest's arsenal?

The thing is, Prayer of Healing is a bit of a tricky subject. It was back in TBC and it still is in WotLK.

The answer is

a) Yes, absolutely, it is a very important tool in a priest's arsenal

and

b) No, you shouldn't use it very often

I'm talking about raids here, not 5-mans.
PoH gets worse as you get more groups. It's also better on 10 man than it is on 25 mans.

Now bear with me:

The reason you shouldn't use it very often (in 25 man raids) is because it has significant drawbacks that make it vastly inferior to Circle of Healing:

1) It is very expensive
2) It is only group-wide, reducing its viability in raids, since your target's group needs to be within distance to receive the heal and nobody outside the group gets healed. Compare this with PoM and CoH which are raid wide, and "smart" - PoM only heals when someone takes damage, and CoH picks the lowest-health targets within its radius regardless of group.
3) It has a long cast time that makes it inferior to druid healing/chain heal/CoH and PoM, and makes it problematic when movement is called for etc

The reason it's still a very good spell is that we also have other tools that enable us to use it anyway.

1) Macro it with Inner Focus and the mana cost is gone AND it has a +25% chance to crit, healing for that much more
2) In raids it is useful on melee groups where the whole group is standing in the same place
3) Serendipity greatly reduces the cast time

So, with a 3-stack of Serendipity, Inner Focus off cooldown and the whole melee group at low health and not getting chainhealed before you finish casting – it is one badass mother of an AoE healing spell.

There are several fights in ICC (particularly in the Plagueworks) where Prayer of Healing can be used to maximum effect. But it is situational and it will, if used often, mostly produce a very big, slow, expensive overheal. Which is bad. It also gets worse with more healers, since I doubt your druids and resto shammies will allow a whole group to get low enough to fully benefit from its heal without topping them up. Again, the smaller the group, the better it is.

Sadly, CoH and PoM spam, as displayed by the Holy priest in question, is the best way to heal 25 mans as holy at the moment (I'm obviously talking about raids here, in 5 mans you have to also tank heal, and you only have one group to worry about so the CoH raid-wide smart heal isn't as overpowered). For pure raid healing you'd skip all the Greater Heal talents and just go for CoH/PoM spam with renew spam in between cooldowns and SoL proc Flash heals where needed.

This unfortunately made my guildie very sad.