This is for mages/shamans because of their AOE posion/rooting skills, it is what makes this powerleveling technique work, basicly all you do is run around making a train/finding enemies then hit them with AoE posion, this takes off no exp and leaves the monster very, very weak most of the time. All you have to do is let the person you are powerleveling open fire or smack the hell out of whatever monsters you have used this technique on.
The beauty of this strategy is that the person your are powerleveling gets the full amount of exp very quickly.
I would suggest that you only do this on monsters that aggro and are relatively slow, i say this because it will keep the monster on the caster and not on the person your powerleveling causing them to come out on top and not get owned by the mobs
(Also a monster this works great with this is the Lirein, off of them you could probly attain level 20 in a day)