Clean the registry and do not save the results. CCleaner is awesome and its registry fixes do indeed speed up the computer and make it more stable (ie. if you have freezing or blue screen issues and you run the ccleaner registry cleaning portion it will often eliminate said issues)
IMO, it is best to save the registry. You don't need to decide what to save or not save, as saving a copy of the registry saves it all. It is very easy to corrupt the registry and if it gets corrupted, it's quite possible that your system won't boot.
There is plenty of info out on the web that supports the fact that cleaning the registry does NOT speed your system up nor provide any real benefit. I would not recommend running the registry cleaner for someone that claims to be computer illiterate.
Well yeah in a way. If you test drive software and then uninstall them, a lot of them don't do a through job of removing all remnants of the software.
Removing reg entries seems to be one thing most don't do.
Using a 3rd party uninstaller like WISE uninstaller will get rid of what is normally left behind. It has Forced and Safe uninstall modes. Safe mode does a normal uninstall. Forced has it take a real close look for anything that is a part of that software and presents it to let you decide if it needs to go.
I have used Forced to remove some software that doesn't have a good uninstaller routine. Like WAMP. It has an awful uninstaller. Leaves a lot of trash behind. WISE sweeps, mops, and squeegees the windows. Then spritzes air freshener.
Reg cleaners like CC become redundant. But still it's better to be safe than sorry. If you're not sure, don't bother with it.