I find the hilarity of Confuse to outweigh the cost of any lost XP.
Confuse a Rikti Communications Officer and he spawns a confused portal, which then disgorges confused Rikti, the chaos is causes is hilarious.
Having a Longbow Warden Fort yourself or one of your teammates, or impale their own with spines, or irradiate them. Too funny.
Having Scirocco clock Night Widow during an STF was priceless. Granted, that also caused the Tank to lose agro and nearly caused a team wipe, but in the end we still prevailed.