This is kinda a dupe, more of common sense.
Well, I was running SM today, and well there was this person who was attacking us. He kept healing himself! And my bro was running it with me too, and he kept saying 'Stop it from healing himself!' but after we killed him, I got twice as much xp! Does anyone know why?
The exp system is based on the damage system, and the more damage you do or your party does, the more exp you get. So whenever you find those mobs that heal themself, let the heal themself, and get a healer to heal you too, you'll get more exp. So just beat the crap outta the mob, let em heal, then do it again. You'll get more exp. And even more if your rested!