Im in a game where its not always the best idea to deal lethal damage. Basically those who rule are corrupt but not the town guard doing their best to keep the city safe. So trying not to kill the town guards and stuff.
Merciful spell is wonderful in that regard.
You can alter spells that inflict damage to inflict nonlethal damage instead. Spells that inflict damage of a particular type (such as fire) inflict nonlethal damage of that same type.