And to answer your last question, I would not just automatically delete them...  Best to look at them first to see what they contain..

FE

Disk clean up can compress those files that you have not used/accessed for a LONG time.
Compressing these files will greatly save hard drive space.

If later you decided to open/access those file, it would take considerably longer to do so.
It is like files in a zip file, after you compress your files, it takes longer to open them,
but be assured, they are still there and available for you to use.

Thanks for your comments, but I still feel rather uncomfortable with the situation as the Disk Clean-up process not only runs the Compress Files routine, but then puts it in the list of items that can be deleted...along with Temporary Files, Recycle Bin, etc.

And how does Windows decide what is an "Old File"...and do these files include data files created by the user or just program files?

Based on the comments above, it seems that it is quite possible and easy to delete files that you had kept for archival purposes.

Like I said before, my philosophy is to NOT delete anything unless I know exactly what it is...  Exactly for the reason you mentioned in your last sentence.  In fact I will not use the Disk Cleanup feature at all...  I do all the tasks manually, for piece of mind.    As far as 'old file', I believe that is determined by the date/time stamp on the file.  

FE

I did a little more research on the web and found the following explaination about Compress Old Files.

"Unlike the other categories, Compress Old Files doesn't delete any files from the drive. It compresses files that Windows hasn't accessed for a specified period of time. The files are still available, but there will be a slight increase in access times because the files will be decompressed the next time they are accessed. Note that when Compress Old Files is highlighted an Options button appears. Clicking it will allow you to set the number of days to wait before an unaccessed file is compressed."

Before reading this I thought that including "Compress Old Files" in the Disk Cleanup routine DELETED files that had been compressed. Now I understand that this is how the files GET compressed.

Yea...  I think that was what we were trying to tell you..  sorry if we confused the issue, but I think you have got it nailed now...  :)

Thanks..!!

FE