There is a feature that I would appreciate very much in Defraggler, and that is that it could defrag the disk empty space.
That is, to 'simply' move all files so that one is placed right after the other. That way, the empty disk space would be pretty much in one big chunk (apart from the files that Defraggler can't move).
I would make that a separate option though. For example, another 'Defrag empty space' button next to the Analyze and Defrag buttons .
Defragging (or in this case, Defraggling ) free space requires extensive hard drive paging and quite a bit of file movement. It's not anything particular about Defraggler or your hard drive that causes this operation to take so long, it's just the operation itself is quite intensive.