Temporary files are files that are generated from browsing the web, downloading files and update, or from various applications. Over time, these can accumulate as well as fragment the hard drive. It is a good idea to clean them out at least once per quarter, and even better at once per month.
How do I clean them out? The easiest way is to use a program such as CCleaner to clean them out. I run CCleaner to clean my own personal computers once per month. This program will help clean up your hard drive.