Since WordPress 2.6, everytime you save a post, it is saved as a revision. All previous revisions are also saved. So, 10 revisions to a post will end up with 11 posts in the database. If you don’t need this revision history, and want to slim your database, add this code to your functions.php file:
define('WP_POST_REVISIONS', false);
Now, if you database is already full of previous revision, and you want to delete...