WordPress has a nice feature. The Post Revisions.
If you need it it's very usefull but if you don't it's a waste of space.
Every time you save a post or it does an auto-save WordPress writes in your data base.
In my case I don't need that Post Revisions so I will disable it.
Open your config.php file in your root installation folder.
Paste this line:
My real case: with this blog, after writing about 10 posts WordPress saved into my data base about 150 revisions.
Do you use the Post Revisions feature?