High-end cameras often have several peculiarities and using one of them is reason enough even if you don't use the others.

My main reason to use my Minolta XM is the mirror lock-up with tripod work. Other will use it for its interchangeable viewfinder, or its interchangeable focusing screen, or its general ruggedness.

Other reasons for using high-end cameras could relate to general quality - features: seeing aperture and shutter speed in the viewfinder, seeing in the viewfinder the shutter speed selected by the camera and the one suggested by the camera, ergonomics of the camera, general quality of shutter and especially of viewfinder (brightness, magnification). Quality is never redundant.

I find general viewfinder quality very important, possibly the most important quality feature in a camera. That's probably why I love so much my Minolta X-700. Its other specifications are pretty normal, but the quality of its viewfinder is pretty impressive.

Still, the X-700 lacks mirror lock-up and that's the only reason why I bought the XM (besides GAS).