EDIT: This post has originally been sent to starting out - what is safe to fix in registry as simple comment. Moderator DennisD has moved it here.
Thanks for the information given Moderator DennisD. However, I'd like to add a few comments.
First: Regardless of the fact that CCleaner itself can create registry backup, it is also possible to backup Registry via (1) System Restore and (2) Windows Backup utility.
Second: Although I use CCleaner and love it as a good cleanup utility, I consider its Registry Cleanup module unsafe and dangerous. I have spotted multiple cases in which CCleaner deletes valid Registry entries. For example, CCleaner deletes some valid per-user file associations (such as those created by ACDSee) under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.
However, there is no point reporting these issues in this forum: Any such report in Bugs subforum is shot down immediately. Developers of CCleaner seem to be of the opinion that Registry Cleanup module is only for advanced users and not everything that it finds is junk.
Personally, I use another product to safely cleanup registry and compact it. (Is it acceptable if I name it here?)
