used in very low light situations or if you are trying to get a special effect in your picture with a lot of movement.
what is shutter speed used for?
extremely fast shutter speeds (something like 1/1000s and faster) would be used to freeze all movement in a scene, but this can only be done in brighter lighting conditions due to the fact that the camera sensor is only exposed to light for a very short amount of time.
extremely slow shutter speeds (something like 1s and slower) would be used to add a lot of movement into a picture, but this can only be done in darker lighting conditions otherwise your image 