I just bought a commuter with disc brakes for the stopping power, particularly in rain. I had avoided riding in rain too much. Now I not only don't mind getting caught in the rain, but start out when it is raining.
I think it is very important to be able to stop well on a street bike due to unpredictable motorists and pedestrians.
With a trail bike, it sometimes seems better to not go too slow or risk getting bogged down. Stopping is important, but I think the disc brakes off-road are more for mud and wet than the need to stop a lot.
Road bikes don't want to stop at all. They are light and built for speed in a straight line on a smooth surface with no obstacles or surprises. Each type of riding is great in its own way. I still have my old hybrid with rim brakes and sometimes do short trips around the neighborhood when there is no chance of rain. It does feel weird using rim brakes after getting used to discs.