I guess it also depends on how you play your NPCs/Monsters.
A large proportion of my encounters finish with the surviving opponents running away so if I offered less XP for this they'd probably never get full XP.
I still remember the old Morale systems, and though I don't still roll for morale, if it seems in character for an opponent to flee, they'll flee. Mostly this is out of realism, only fanatics and non-sentient creatures are likely to fight to the death.
Also the good aligned characters in the group like to be able to show mercy. They already have enough worries with the whole, "can we trust their surrender?" thing without having to settle for less XP for good roleplaying.
A large proportion of my encounters finish with the surviving opponents running away so if I offered less XP for this they'd probably never get full XP.
I still remember the old Morale systems, and though I don't still roll for morale, if it seems in character for an opponent to flee, they'll flee. Mostly this is out of realism, only fanatics and non-sentient creatures are likely to fight to the death.
Also the good aligned characters in the group like to be able to show mercy. They already have enough worries with the whole, "can we trust their surrender?" thing without having to settle for less XP for good roleplaying.