Cover is a great skill, it's situational tho. It shouldn't be used whenever, only when you feel it'll help.
I personally only use it on my healers, or on rare occasions, the MT, if I'm off tanking.
On DPS? No, never.

There is ABSOLUTELY NO REASON for DPS to take damage.

I might sound a bit rude towards DPS, but it's really just that.
If a healer doesn't get out of AoE, it's 90% of the time to heal someone else, I will Cover and take his damage, gladly.
If a MT can't get out of AoE, it might be due to his weird positioning as MT, not a good excuse, but if it's reasonable and manageable HP wise for me, I'll Cover and soak the damage.
If a DPS doesn't get out of AoE it's because of... There is no justifying for that. I don't care what spell you were casting, how much damage you could've done. If you're dead, you do 0 damage, that should be clear to you. I will not take additional damage because of people being ignorant.