The side effect of changing the shutter speed is the amount of motion blur. To convey motion, use a slow shutter speed (shutter open for a longer time). Anything longer than a 1/4 second is considered kinda slow. See how the water in the right image has a silky look. The shutter was open for four seconds, and the water’s movement got blurred. Conversely, if you want to freeze the motion in your scene, use a fast shutter speed.