Can't speak for NWN, but I know in ToEE, Coup de grace is very useful for finishing off trolls once they are on the floor.

Coup de Grace is a move that a rogue can perform when his/her enemy is alsepp/paralized etc. It is a killing blow.

Since your also Playing SoU I will move this over to that forum.

Cheers

Not just a rogue either, any class can do it. However, it won't work with spells or missile weapons.