Bulb setting can also be used to open the shutter to 'wait' for something like an externally triggered strobe or flash.

If you wanted to experiment with motion capture of a ball bouncing, you could set the camera up on a tripod in a dark environment facing a dark backdrop and open the shutter and drop a ball in front of the camera while triggering a strobe or flash. Then close the shutter. Where you might not have complete control of synchronization of flash or are unsure of low light or an event it can be real helpful.

Say you wanted to capture the streaks of light on a highway or street and wished to have a light from a vehicle extend only a certain distance in the frame, you could just 'turn on' the exposure when you desired and then turn it off. In these cases a Polarizer of Neutral Density Filter can help to lenthen exposure time and many times cut the sensor bloom effect. If you have night shot (usually takes a dark frame and subtracts the hot pixels) this might be a good combination for those longer exposures.

This is not quite as simple as it sounds here, but these are some things that can be done with a bulb setting.