Composition is the way in which something is made up of different parts , things , or members. But putting photos together is the best way of composition because the way you need to put photos together. Famous photographers they always use composition everyday of their life. The reason why using composition is very important is that highly trained photographers can put their best pictures together. The links below shows that most of the photos that have been taken by its photographer is that that person used composition.
http://www.youngphotographersalliance.org/http://photography.nationalgeographic.com http://photo.net/gallery/