The Windows* registry is a database that lists all of the configuration settings that determine how Windows looks and behaves. Sometimes, settings that are no longer needed will remain in the registry in case they're ever needed again. There's nothing unusual about this, and this data is small in size.
Some products available for free on the Internet suggest the registry needs regular maintenance or cleaning. Although a registry setting can become corrupt on occasion, in general, the registry is self-sufficient. If you decide to install a registry cleaner, be sure to research the product and only download and install programs from software publishers that you trust.