A registry cleaner is a software product designed to identify and remove unnecessary registry keys in the Windows registry. The registry stores important information about your computer, but it can get corrupted over time. Makers of registry cleaners claim that using their programs will make your computer run faster and reduce crashes and errors. As long as the program you use does not contain spyware or remove information that's required to use the computer, it's safe to use.

On the Other: Probably Unnecessary

Articles from as far back as 2005 have stated that registry cleaners are most beneficial for older versions of Windows. So if you're running Windows XP or newer (Vista, Windows 7, etc.), the programs probably won't do much to improve your computer's performance. There are probably other reasons why your computer is crashing or running slowly, such as viruses or using too much memory, that the registry cleaner will do nothing to fix.

Bottom Line

Always read reviews of software before downloading and using it. Bogus software may harm your computer and/or make the problems you have with it worse. Try other solutions, such as running a virus/spyware scan or defragmenting the hard drive. If you still have issues after using a registry cleaner, consult a professional for technical help.

Source:

RegistryCleanersReviewed.com: Registry Cleaner Reviews

Information Week: Testing 10 Windows "Registry Cleaning" Software Packs