I'm not a fan of it interfering in people getting credit for Nathanos, or being unable to loot IC rares because of it, these are the only instances I would refer to as griefing, and then only because of blizzard's poor implementation preventing people getting credit and loot.
Edit - also, I completed Exile's Reach and did NOT get the immunity buff that was promised, had to get the hell out of SW with my level 10 quickly.