By default, any print jobs sent to a printer will be temporarily spooled to a folder on your hard drive. Usually these files are then deleted when the job has printed. Sometimes when things go wrong, however, these temporary files can be left behind, eating up disk space. If you are not expecting anything to be printed currently, you may safely delete any files found in that folder. You can find the folder in 'C:\Windows\System32\Spool\Printers'. It doesn't hurt to take a look in there occasionally when you need to free up disk space.