Zoom and prime lenses both have their own purposes and respective pros and cons, although beginners typically default to using zooms, particularly since most kit lenses are of that variety. There are a few properties than should make you consider grabbing a prime lens instead, however, and this excellent video discusses one of the subtler reasons using one can benefit your photography.
Coming to you from James Popsys, this awesome video discusses the benefit of using a prime and how it forces you to be more deliberate and develop your compositional eye. Advocates of prime lenses will often say that you can "zoom with your feet," but this is a bit misleading, as different focal lengths will produce different perspectives, even if you adjust your position so that the subject is the same size in the frame. Rather, a prime lens removes the convenience of a zoom, which allows you to stand in one spot and create several different compositions. In doing this and thereby forcing you to move throughout the scene, you will be forced to put more thought into your compositions, and you might find a shot you would not have been aware of otherwise. Check out the video above for the full rundown from Popsys.