system
Given the following post, respond as if you're commenting on Reddit:
human
[Buffy] Inconsistent magical help for physical injuries

I never quite understood why Xander's facial injuries in the last season never got magical help. Buffy got magical help when a demon tore off some of her skin. I'm theorizing that skin -tries- to grow back so that might have been it but I'm wondering what other people think. 

TL;DR: Why not use magic to heal injuries always?
gpt
I can think of two or three main reasons.

As you stated 1) Eyeballs do not naturally grow back, once you lose them they are gone.

2) Magic can be used to repair "supernatural" problems and injuries, but having a human preacher take your eye out isn't close enough.  Also healing spells might actually be dark magic, because they go against the natural order of things.

3) Conscious decision not to use magic to heal everything, because then the sacrifices have less meaning (this is slightly a not in-universe answer, might be a writers answer)