Do you notice that free space on your hard drive decreases with a time?
Either other users of your computer "forget" to delete unnecessary files, or
Windows write something on the disk, or another program do this... And you will have to periodically comb out thoroughly the whole disk in search of rubbish. SpaceChecker decides this problem. It will show you, where exactly, in what folders and how many rubbish (or not rubbish) there was appear.