I am using version 1.15.163, and when opting for Quick Defrag on my c: get the message:
Empty Recycle Bin before defragging?
This will give you an extra 625 MB of free space.
As I don't use the Recycle Bin at all I was wondering about that, so checked all drives. I have nothing in the Recycle Bin on any drive, so where this amount comes from is a little riddle to me...
I do have a c:\temp, but that contains a totally different amount of files. (More like 8 GB.)
There are no other directories in the root of C with that size.
And while typing this I'm wondering why "c:\Documents and Settings\<username>\Local Settings\Temp" isn't emptied before running defrag?