When you run disk cleanup, a dialog will show all temporary files that can be removed without affecting system functionality and stability. If you click on the "More Options" tab, you can additionally remove installed Windows components that you do not require any more (e.g. games). Or you can remove applications, that you do not use any longer. This usually saves a lot of space. When you click OK, all checked options on the "Disk Cleanup" tab will be processed and removed. Keep in mind that temporary Internet files will also be removed (if checked). Maybe you are accessing Web sites that install some applets or other components. These have to be reinstalled the next time you visit the site.
This was first published in June 2002