For each saved edit made to a post or a page, WordPress saves a revision in the database. This can really increase the size of your database when your working with a lot of posts or pages. WordPress has a built-in revisions option which you can set in the wp-config.php file. You can also disable revisions altogether.
To disable revisions completely:
define( 'WP_POST_REVISIONS', false );
To limit the amount of revisions:
define( 'WP_POST_REVISIONS', 3 );
You could also just download the Revisions plugin
That way you can set the revisions number from the admin section.
WordPress also saves an auto-save revision when editing a post or page. You can set the interval of this auto-save function. By default it saves a revision every 60 seconds.
Set the auto-save interval:
define( 'AUTOSAVE_INTERVAL', 150 );