It has also become fashionable to slow down the shutter and then move the camera to give intentional blur by moving the camera whilst the shutter is open. Closing down the apature can assist in this but this is often achieved in sunny conditions by the use of a Neutral Density Filter.
On the other hand, shutter speed can also be used to do just the opposite – freeze motion. If you use an especially fast shutter speed, you can eliminate motion even from fast-moving objects, like birds in flight, or cars driving past. If you use a fast shutter speed while taking pictures of a water, each droplet will hang in the air completely sharp, which might not even be visible to our own eyes.