For example, if you have 1 post and it has 10 revisions you could be storing up to 10 copies of older or unused data in your database, which will increase the size of your database for sure. You can learn more about Post Revisions by clicking here.
Now we know that these useless post revisions are just wasting our space. You can't delete these revisions manually, but the oldest revision is automatically deleted if there are more than 25 revisions.
Better Delete Revision:
Better Delete Revision is a great plugin to delete all useless post revisions off your database, it also deletes other database content related to each revision such meta information, tags, relationships, and more. While Better Delete Revision hasn't been updated in over 2 years, but it is compatible with the latest version of WordPress (3.x).
Here is the original description of Better Delete Revision:
Remove and delete old revision of posts, pages and related meta content completely then optimize Database: reduce size and optimization to speed up!
Installing Better Delete Revision:
- Click here and download this plugin. Visit your WordPress' plugin page and install this plugin.
- You can also install this plugin from your WP's plugin directory.
- After installing, just click on active.
After installing, a new option will appear under the Settings tab. Not here is how to delete old post revisions:
- Visit Settings > Better Delete Revision
- Click on "Check Revision Posts" option. It'll show a list of old posts revisions.
- In the bottom, click on "Yes, I would like to delete them!" button and it's all done.
WordPress’ database queries don't retrieve revisions, so the number of revisions has no effect on the queries, but it's a great way of keeping your database clean. The only time the revisions are retrieved is on the edit page of the individual post.