I assume that temples could play a role in creation (or finding) some special items. Here You can see the legendary Ghostbane blade. It references Bogenheim Abbey. A church (or an abbey) is basically a temple, a building of worship.
Alternatively temples could serve as a spawning grounds for the refreshed ancient Undead. Ancient enemies require ancient place of origin. It could serve necromancers as a place to conduct their dark arts, especially if the ancients were keen on burying their dead in a special places (which could be pretty much the same as the Christian practice to bury people at cementaries, the so-called “Holy Ground”).
