What ccleaner does is hardly minor as essentially it is no different to what has been said, the data isn't deleted period by any of the methods, just the references.
Unless you go the extra mile and use wiping software the data still remains whatever method you use.
CCleaner cleans the list or restore points, so they can't be used after the cleaning, but the files are still left untouched in the HDD, so for the purposes of this topic, that's not useful enough.
So system restore isn't actually deleting anything other than the references, so for me nothing different to ccleaner, the references aren't there so the restore points can't be used and that really is what I feel is important, to prevent old software and possibly malware being restored.
DavidR, we are talking about two different things. You are talking about "references" of the file system (such as the FAT in a FATnn filesystem) when deleting any file. When CCleaner deletes the "list" of available Restore Points, no file is deleted in the System Volume Information, and no "reference to files" are deleted pointing to files in the System Information Volume.
CCleaner doesn't touch the files, at all. It only deletes the
list of points, so you can't see it when you want to select some restore point (so to apply it), except from the last restore point. CCleaner doesn't touch the files and not the "reference to files" (i.e. in FATnn, the first reference to the first cluster where the actual file is located).
In other words, when the "Free Space" utility of Windows is used, or when disabling System Restore, the files are deleted (i.e. the first "reference" to the file is marked as available); but when using CCleaner, the entire files will still be there.
Meaning, after CCleaner, if you search the files in System Information Volume (with the appropriate permissions), you will still see the files (all the files representing all the restore points). But when using the "Free Space" utility or when disabling System Restore and rebooting, the same search of files should return just one set of files representing only one restore point (or none).
This means that, after CCleaner, avast would still find files in System Volume Information just as before, even when the restore points were "deleted" by CCleaner, and there should be not much more free space.
OTOH, when the files are actually deleted (i.e. their "references" in the FAT) using the "Free Space" utility or by disabling System Restore, there is in fact free space gained in System Volume Information. This is not accomplished when using CCleaner to "delete" the list of Restore Points.
In neither case the "deleted" restore points can be used (applied), but with CCleaner the real files will still be there.