While I don't mind on most trash mobs, I will usually be on the lookout for an aoe that I can stun thereby preventing the need for both me and the dps to move out of the aoe. It's kind of annoying when the DPS uses it without a second thought.

A great example is the crazy golem at the end of Qarn or the final boss. Many times when I go to use my stun when he follows someone with the beam he is already immune.

Also sometimes when I do a mass pull and the damn mobs are shooting aoes there are sometimes I just get tired of going in/out so I stunnlock them.