Your focal length isn't just for getting closer to subjects, it can completely change the feel of your image and knowing how different focal lengths affect your image can help you to pre-visualiseyour shot even before you've taken it.

This article from Digital Photography School talks about 5 of the classic focal lengths, well worth a read!

http://digital-photography-school.com/5-important-focal-lengths-to-know-and-the-benefits-of-each/