allan is correct, if you don't know what you're getting rid of, your better off leaving the registry alone.
for instance, I use a registry cleaner that will in fact nuke my help and support unless I exclude the "help".
now, if you want to experiment, not only are there backup files, but again most of these programs send the files to the recycle bin, so, if the backup file doesn't work, you can return the files from the bin.
be forwarned, however, some items might become corrupt, adn you won;t know it for some time to come.
for instance, some restore points can become corrupt from this process...this has happened to me, and I presumeably know what I'm doing.
since that time, I ndon't clean the registry unless I'm very satisfied that I won't be needing a prior restore point, and then, afer I clean, I create a restore point immediately