Do you know who the awesomest person in a 10man raid is?
No, it's not the tank.
Not the raid leader.
Also, not me (I'm second though; Nice try you brown-noser!).
It's the Third Healer.
See, the Third Healer is the magical person who agrees to bounce back and forth between a healing and a DPS spec at your every whim. When you're testing out new strategies and logistics on new bosses, that Third Healer is the lynchpin to success.
When I'm running a raid (I use the word "running" because I don't technically lead, because that requires me to click things like "give people assist" and mark people and that's totally hard, and also, I get really mad when people talk over me, and then I shut up and pout, so it's usually better if someone else takes the official leading role, even if I'm bossing him around from the background... ahem), I like to try new bosses with an eye for surviving as long as possible on our first few attempts. I don't care about enrage timers; I want everyone to live as long as possible so that they can see as much of the boss fight as possible, and get into the swing of things.
And that, my friends, is where the Third Healer comes in.
Our Third Healer is a Resto/Elemental Shammy. He is the perfect Third Healer. What does it take to be a great Third Healer?
Ability to do solid DPS in one spec
Ability to do awesome Healing in another spec
Ability to properly gear both specs
Patience with a very annoying RL who keeps telling you to switch things around
This shammy is the best at all those things. The other two healers in our raid DO have off-specs, of course. We *could* DPS if needed. I have a very nice Shadow set, and though I'm not going to top any meters, I could probably... well, still come in dead last but not by a huge margin. The druid healer who sits next to me, however, isn't even hit-capped on his off-spec.
The Shammy in question, however, is never a waste of resources. He can top the DPS when that's his assignment, and he can also top the effective heals when he's healing. He can tank heal if needed. He can raid heal if needed. As a shaman, he is not particularly strong on the mobility front, but that's a feature of his class - not him as a player. And I don't fret about that too much, because the Disc Priest and the Resto Druid have mobility coming out the... well.
Because he is constantly switching back and forth to help us out as we learn new bosses, I have a Third Healer loot rule. That means that his main-spec and off-spec are one and the same for loot purposes. We don't really have strict rules in our raid, it's mostly based on courtesy - if someone has already won something, they can still roll, but we'll give priority to someone who hasn't won anything yet (for the record, this is sooo much easier to do in a 10 man raid!). We do, however, give priority to people's main specs. For the Third Healer, however, he can roll on anything that would benefit either of his specs.
It sure helps that the person who made that rule, however, is one of the healers against whom he will be rolling for items. Not sure how well that would go over if the other healers didn't agree with this philosophy.
Anyway, the point of all this, is that if you are starting to put together some ten man raids, if you are learning new fights - bring someone who can deeps AND heal, and is flexible enough, and willing enough to do both. And don't screw them on loot - you WANT them to maintain a good healing set as well as a good dps set. And that's not always easy!
That Third Healer is integral to learning new fights, especially if you're a pretty casual bunch.
A toast to our Third Healer, who helped us learn every boss in ICC so far!