Kingdom units get stat boosts on kingdom-type land, and stat penalties on empire-type land.  Visa versa for empire units.  So if you're intending to fight a close battle against a faction of the opposite alignment, turning the battleground friendly might be a strong move.

It sounds like a great spell for the reasons stated, but I was actually trying to use it at one point to clear out a great number of forested tiles so I could put a settlement there. I thought revive made trees and des. got rid of them. Don't know if a spell like this exists but it would be great to have one.