The attendance risk
While I say that each person in a 10-man raid is 10% of the performance, that's not actually true. A tank is half of the tank group, a single healer is 30% of the healer group, and each DPS player is 20% of the the raid's damage. That means that proportionally, every player is absolutely, incredibly important to the overall outcome.
A single person's absence on a raid night means more than 10% of your raid; it means that you're out a portion of that raid role. While you can usually PUG or network to find an extra DPS player, if your raid is missing a tank or a healer, you tend to be out of luck. If two people from the healer and tank corps are missing, you're almost definitely not raiding.
The natural solution to this issue is to have slightly more than 10 people available to raid. Maintaining this overage will help make sure the raid if full every night. Let's talk about that a little bit more in a bit.
Risky raid composition
Raid composition is a science unto itself. In a perfect world in which you can have any class you want raiding, you will mix your raid to bring just the right mix of buffs and debuffs. You'd avoid having any more melee than necessary to provide those buffs, so that you cut down on the number of Chain Lightning attacks hitting the raid.
The reality, however, is that most of us play with our friends. As a raid leader who's married at least 10% of his raid and is very good friends with most of the rest, I try and make do with whatever classes those raid members want to play. We do a little bit of juggling to make sure we have enough healers and tanks, and voilà, we have a raid.
But if someone is missing on a particular night, that house of cards comes tumbling down. If a particular class is vastly underpowered or a raid role penalized in a fight, then we struggle to get by. Most raids are already very tight on tanks and healers, and the "pure" classes can't pitch hit in these roles.
So now let's solve this problem.
Shaman and druids, oh my
As annoying as it is to say so, the best solution for 10-man raids is to be druid- and shaman-heavy. Hunters are a close third, and then paladins fourth. Here's why.
Druids can perform any raid role; they can be ranged DPS, melee DPS, healers, and tanks. While not every player is geared and prepared to play those roles, the class itself is capable. Shamans are a pretty close second, being able to heal or do either version of DPS. I don't include paladins in these most flexible of classes because they can tank and heal, which is awesome, but no raid leader is going to suddenly say, "Dammit, we need more melee DPS or Omnotron isn't dying!"
Hunters are in a pretty interesting spot right now, because they can bring so many different raid utilities through their pets. Need a physical damage debuff? Bam! Demoralizing Screech. Lacking a shaman or mage? No problem, here's your Ancient Hysteria. (Also a good chance to listen to some Def Leppard.)
Stacking shaman and druids lets you move raid members relatively effortless through the roles. If you're missing a tank, one of the boomkin becomes a bear. If you're missing a healer, then that elemental shaman now embraces life as a healer.
Is it ideal? Probably not. People choose the specs they want to play with almost the same strength they choose classes. However, when it comes down between "respec or we don't raid," most players would rather respec.
The bottom line is that every hybrid in the raid should embrace flexibility. If you're a priest who refuses to heal, you're not helping your raid. In a perfect world, everyone would be able to do exactly what they wish. However, when raiders start calling in sick, you have to man up and slap on healer face; get it done, and hopefully next week you'll be back to DPSing.
It's hard, if not impossible, to induce flexibility in a 10-man raid by having an understudy for every raid role. That would mean you'd have three people "sitting out" every night, and even if you rotate who sits out, that still sucks for anyone who wants to raid seriously. Flexibility is the answer.
Make your raid as flexible as you possibly can. And then on nights you're short, PUG in ranged DPS while your experienced, seasoned members fill in the tank or healer roles.
Ready Check shares all the strategies and inside information you need to take your raiding to the next level. Be sure to look up our strategy guides to Cataclysm's 5-man instances, and for more healer-centric advice, visit Raid Rx.