I make it a point of never intentionally hurting my party members, just for roleplaying purposes. In PnP, if you cast a fireball on your tank, your tank would turn around and kick your butt (i.e. turn hostile like your summons do in BG). Besides, they are supposed to be my friends. However, in evil parties, all bets are off, especially if I intend to "off" the poor sod.