I shoot too much film to have time to contact proof them all. But I'm getting better at it.

To me it's a great interpretive tool. It really tells me how I'm doing with my exposures and film processing. To make it truly worthwhile, the proofing should be done on the same paper you print, but I can't afford an 11x14 sheet of Ilford MGWT for every roll of film I shoot.
All contact sheets are minimum exposure for getting black through the film edge. This is another situation where using the same film over and over again really helps. I have the enlarger head height recorded, the bulb power, lens aperture, and exposure time noted for my cheapo Arista RC paper I use for this purpose. So that every time I make a contact sheet, the exposure time is exactly the same.

I find it useful, and wish I had done it on all my rolls to date, just to learn to understand film processing and its variables faster than I did.