It's an annoying wow habit.

As a healer, I really don't like it. These are usually the tanks that don't know what mitigation is, and I'll blow my load trying to heal them and not get any regen between pulls.

And of course I don't say anything because people are sensitive snowflakes that'll throw a stink if you try to tell them how it's done here. This ain't wow. Quit playing as if it is, please.