Good point. I'm extremely compulsive, so I NEED to have a 100% viewfinder. This also means I've filed my negative carrier on my enlarger, and I leave my slides unmounted which is fine except I can't project them.
It's probably easier for most to use a viewfinder with 95-97% coverage.
Or use 100% for all except slides, then use a 97% viewfinder camera, like an FE or? I never found it that hard to allow some space when shooting slides with my F3.