Recently I installed plugin called Delete-Revision and noticed that every post has registered few post IDs. I usually use save drafts and update post a few times when I write a post. Here's the screenshot http://i.stack.imgur.com/0pqgx.png . As you see I have 53 posts and Wordpress already registered 646 post IDs. How can I stop it and clear unused IDs?
You can stop WP creating revisions by adding the following to your wp-config.php:
define('WP_POST_REVISIONS', false );
You can replace
false with an integer if you just want to restrict the number a maximum number of revisions.
You cannot turn off drafts. You can reduce the frequency of autosaves if you wish, but WP only keeps one autosave per post anyway:
define('AUTOSAVE_INTERVAL', 160 ); // seconds