Often, the best option to fix these problems would be to reformat your computer and reinstall your OS, but since most of us don't plan on ever taking this drastic measure, we don't obtain a recovery disc or thumb drive. In other cases, your Mac can be experiencing some major malfunctions: constant crashing, locked controls, slow boot times, missing files, etc. At one point, I realized that there were plenty of files on my Mac that I didn't need any more, but too many to delete individually. As I've said before, slowing down is not an option for me.