[quote=Fabricant451]
What, like money? Are we not getting EXP from these kills?
[/quote]

You get EXP by defeating these spirits. Killing or not gives Morality points to the ending. Killing anything else will probably not have the same thing, these spirits are special however.

No cost isnt money xD bigger than that.

Also depending on how you beat these spirits, depends on the reward.