CCleaner is fantastic as a general tool, but manage your expectations.
1- cleans misc unwanted files from your computer including hotfix uninstallers. A good analogy would be that it sweeps the floor, does not mop it.
2- cleans the registry of entries that are no longer used such as "unused file extensions". Same sweeps instead of mops.
3- offers a method of wiping unused space on any attached hdd, maintaining the OS and working data. From 1 - 35 overwrites, this locks the car door but does not protect you from someone willing to break the window.
4- offers an on/off toggle for start-up programs; although autorun is better.
You can definitely use these as it has no disadvantage.