Oh man, I used to use my grandfather's Leica M-series camera when I was in high school. That was some seriously good glass that he had. It was really great for doing sports shots since looking through the rangefinder, I could see what was outside the frame of the telephoto lens to catch the full action.

I'm a photographer for my school's newspaper and I do the same with my Fuji X-Pro2. The optical finder lets me monitor when the action is coming into the frame, and there's even a small electronic finder in the corner to show me exactly what the sensor sees.