Recently, the makers of MacKeeper, software designed to enhance the performance of Macs and protect them against malware, settled in a class-action lawsuit alleging that the software did not perform as advertised. Users of the software can sign up to receive a payment of up to $39.95.
While the makers of MacKeeper did not admit to any wrongdoing, it's hard not to view their advertising practices as suspect. As PC World reports, third-party testers found that MacKeeper employed alarming-looking "warnings" that there were large amounts of "junk" files on the user's system, which the user would have to pay for the software to "clean up." It turned, out, though, that those "junk" files were completely normal components of the operating system, such as language files, which, while probably not necessary for most everyday users, were completely legitimate and probably had little bearing on the performance of the computer.
This is the problem with software claiming to clean or speed up your computer (other programs include MyCleanPC, MyTurboPC, etc.). It's not as if these programs don't do anything; it's just that they're often misleading about what they do. These applications "speed up" your computer by deleting files they deem unnecessary. Sometimes it works, but sometimes users won't notice much of a difference. Perhaps the larger point is that these programs come with a set of baked-in assumptions on what users need and don't need, which may cause problems for users whose needs don't fit those assumptions.
That's why we don't recommend these "cleanup" applications. There is definitely a place for cleaning up unnecessary files to improve computers' performance, but beware of "quick fix" offers like MacKeeper.