Limit WordPress Post/Page Revisions
by Jason Koning

Reduce your database overhead – reduce it’s size & speed your site up – probably marginally, but every little helps.
//Create a maximum of 6 revisions, plus one for auto-save.
define('WP_POST_REVISIONS', 6);
Pop that at the top of your wp-config.php file inside the opening PHP tag.
Note: you can disable post/page revisions altogether – but I’d recommend against that.