This is a great question. I've seen the same behavior. After a defrag is completed, if you immediately do another defrag, it seems like every file on my hard drive is shuffled around instead of just moving as few files as possible into the consolidated free space. I'm no expert on defrag algorithms, but jeez it doesn't make sense at all to re-shuffle such a huge percentage of perfectly fine files on the hard drive just to defrag a few fragmented files! This just makes it run for a long time too. What gives? I love the graphic display of Defraggler but I'll just go back to the windows defragger if my poor hard drive needs to thrash for hours needlessly every time I do a defrag. It looks like it starts from the beginning of the drive and just blindly moves files cluster by cluster to fit from beginning to end, ignoring the fact that the vast majority of files in there are already contiguous.
