Every time you create a new post or page, WordPress automatically (every 90 seconds) saves a revision to the database. It is recommended ones in a while to clean these revisions.
In the video tutorial below you will found out how to delete (or maybe restore) the revisions kept in the database by using one very useful WordPress plugin called Revision Control. Keeping your DB clean will improve the speed of your site and thus will improve your visitors’ experience. Not to mention the results in the Search Engines. Watch the video lesson and learn how to easily use Revision Control plugin.
Revision Control Video Tutorial and Review