Absolutely, 100% backwards. The tool cannot save space from disk space that is not scanned. Your "not a big win" comment assumes that there is no space left to

Absolutely, 100% backwards. The tool cannot save space from disk space that is not scanned. Your "not a big win" comment assumes that there is no space left to be reclaimed on the rest of the disk. Or that the disk is not empty, or that the rest of the disk can't be reclaimed at an even higher rate.