I have noticed a lot of plugins over the years lack the ability to totally uninstall files. What I mean by totally uninstalling is that when you use your WordPress admin panel to delete the files, it does not always take away the database tables that were installed in the beginning. A couple I can think of up front, are Next Gen Gallery and WP Link Directory.
While it might not seem so important for most people, it is important to remove any resources that you do not plan to use on your webhosting space because it could prove to be a way to hack into later on in the future. If hacked, this can run up your resources and suspend, or with some webhosts, they may ask you to upgrade or say they cannot host you.
This post was submitted by wpaddict.