After extended use of a computer, lots of "trash" can accumulate on a system. From internet cache and orphaned registry entries, to a simple fragmentation of the hard disks. We can go through and eliminate any unnecessary data that may be doing nothing but taking up space on your system. You wouldn't drive your car for several years without performing a tune up, would you? A computer should really be no different. Good thing you don't have to put gas in it however.