Hi ,
I'd like to share with you one of the most essential compositional guidelines I live by. When I'm out shooting, no matter if I'm photographing landscapes, people, action, aerials or travel scenes, I strive to keep the edges sacred.
I just think it gives the photo a cleaner, less cluttered look. It also reflects the notion that you, as a photographer, are making deliberate decisions about the arrangement of subject matter in your frame.
You should always be deliberate about your compositions. Otherwise, it looks like you just weren't paying attention, and that often gives your photos an awkward feel. That being said, there are times when you can get away with having subjects at the edges, but there's a trick to making it work.