This program saved me from a strange error (an 'orphaned file') that no amount of tinkering with inbuilt utilities would fix, including command-line entries used as a 'single user'. I would otherwise have needed to do a lengthly reinstall, as it refused to boot at the time. Not only that, but it fixed numerous smaller errors, resulting in a faster and smoother disk to use. The program took some time to work it's magic, but it was certainly effective.