Repose in dungeons?

[Estellios]

Something worth mentioning is that you don't build further hate on slept enemies unless you actually perform actions against them. So tanks can continue building hate with Flash and your heals won't gain you enmity while the enemies are sleeping.

It's nice in lower level dungeons where you are capped, but at level 50 as people have mentioned, a lot of enemies will be immune and due to iLevel you will likely be overgeared and can just AoE them down anyway. Before that, go nuts sleeping. It's not like MP is ever an issue on trash mobs.