After a while, WordPress blogs and sites can start to feel a bit slow, and this is often a result of a cluttered database. Being a dynamic platform, WordPress stores its information in database tables. As you activate and deactivate plugins, information may be added to existing tables, or new tables may be created that you no longer need.
Therefore, it is worthwhile to try to clean up the database every once in a while. Optimize DB makes it easy for you to do that. Simply upload, activate, and go to Manage > Optimize DB.