Not always a tank's job to mark.

What he was trying to say is that if you're sleeping something you should mark it so he knows not to wake it up, I assume. Usually you use something other than the 1, 2, 3 symbols (IE the chains, shapes, etc).

It's a good way of mitigating damage if the BLM sleeps but... on the other hand... it's a lot quicker just to burn everything down. I guess it depends on how competent your healer is.