For me personally I'm interested in registry cleaners to fix two kind of issues, first one is the remaining-modified settings in registry for software that doesn't have a reset button that saved in the registry, and the second one is the context menu remnants that some software left behind after uninstalling.
The first one I now learned how to remove manually or by deleting the .ini file in AppData folder, and the second one I faced remnants recently that all registry cleaners couldn't find at all while any context menu manager can remove them easily and safely, so I started to lose my interest in registry cleaners.