1.The so-called Temp files/folders in Local Settings which cannot be removed. I understand, a bit, Temp files which, for some reason, are in use (why are they called Temp?), but I cannot understand Temp folders (usually), which cannot be deleted. Why are they there, in first place? They seem to be renewed every day, and are full of subfolders. I have two which contain a total of about 15 MB, but they keep recurring. So, they must be created by some other program. One folder contains a file created by ActiveState, which
.supports cross-platform development tools for dynamic languages such as Perl, PHP, Python, Ruby, and Tcl, as well as language distributions and enterprise services
2. Programs which have been uninstalled long ago, but left something behind. One of them is Dawn, not the liquid detergent, but a program related to mail, which I removed, at least eight years ago. I am told that some nondescript .msi cannot be removed, so Cccleaner cannot delete the item. There is nothing left on my hard drive. I must be some errant registry key. Otherwise, I am told to insert the CD containing the program. I had the same problem with Apple Mobile Device Support (I had two different sized items with the same name). Finally, after a few years, I was able to uninstall such thing. I guess it was placed by iTunes, but an update did not remove the older item.
3. My favorite occurs when I want to delete some item in the above mentioned Temp folder. Even if a single file in that folder cannot be deleted, nothing be be deleted.
I am pretty sure that most people have never tried to do what I have tried to do, but if there is any idea, I will be at peace. I have dealt with this as long as I have had a PC.