Gandalf and his Power

Just one simple Qustion from Film Fan (sadly havent red the books yet)

Why the hell Gandalf use his powers just in few cases, i know that he shouldnt use his powers just because he can, but why does he actually in most cases prefer his sword? I mean in Moria, where he protects The Ring, or in Minas Thirith, where his powers could get Gondor more Time..

Sorry if this is a dumb question, and for m English.. 🙃