Aggro, a bit of detail
A specific example of the healer aggro problem comes in Hellfire Ramparts when fighting Nazan. Well, Vazruden and Nazan, but Nazan is always the problem.
For those who haven’t been there, here’s the setup in simple. Nazan is a netherdrake (think riding size dragon) which Vazruden – a twinked Fel Orc – rides. They are constantly circling what amounts to a landing pad. Your party runs up and kills the two orcs guarding the pad, and as the pair come close to the pad Vazruden jumps off and attacks your party. Nazan continues to circle, shooting sticky fireballs down at your party, until Vazruden gets around 20% of health. Then the dragon – sorry, netherdrake – lands and joins the fun in melee.
Remember what I said about the heals, while only half a point of threat per point healed are a threat to all mobs in the party? Yep – the big deal of this fight just became obvious. Nazan has tagged the healer as Most Dangerous and charges. At most three hits later – or one cone of fire – and the party is lacking a healer. As it happens, the common discussion of this battle in various tactics lists is the fact that the netherdrake charges your healer first and what you should do about it.
As a healer, you have two possibilities. First and least preferable, you can do zero heals to the party while they’re on Vazruden. Second, you can do a preemptive fade as Nazan lands. With your threat temporarily at zero Nazan will go for the next highest threat or the closest party member. If you can wait till your fade ends the tank and the rest of the party should have more than enough threat from damage to keep him off you.
Assuming, of course, that your party is decent. But that’s another post.