The old description for the trope (before my recent edit) seems to come across more about complaining about the hero sparing the villain at all
(and a little too specifically about a falling death). The original point of the trope isn't about the Hero not killing the villain out of Joker Immunity
or a misapplication of Thou Shalt Not Kill
, but rather the fact that the villain is now helpless before the hero. It's literally a matter of the type of person the hero is. Is he the kind of person who would kill a helpless (or unarmed if it's a matter of honor) man?
Now when it's done wrong
, that's when the writers fail to apply it universally. Sparing the villain after the battle when you killed Mooks
(or The Dragon
) during it is not
a misuse of the trope in and of itself. Now if the hero spared the villain after blowing up the enemy barracks, then you did something wrong.