Zeu5

While it's true that some of the files may be in System Volume Information or another system directory, defragging actually DOES reduce the size of files. By moving them together on the drive, it removes all of the links that the system has to use to keep track of the segments, freeing up a bunch of space depending on how many fragments there are of that file. Also, the reason you are having to run it repeatedly might be that 10GB's is a little small for manipulating 70GB's of data. So, your theory on it working in stages sounds accurate. But I'm glad it worked out for you in the end.

Defraggler would be a much better program if it included a tool to do a boot-time defrag, able to defrag the MFT and the Page files without damaging anything. There are many other programs that do this, but I have faith in Piriform to find a solution so I can continue using their products for maintenance.

What are the names of the files? They might be system files that Windows wants to be kept in there. Also, this does not belong in this section, for future reference, as this is not a suggestion.

Aethec is right, if you see any fragmentation left over, it's most likely because it's in reserved system space. There are many good utilities for defragging these places, but I personally leave them be if it's on a machine I use all the time. For example, I use my desktop for gaming only, and I do things like that all the time so I have it at the highest possible FPS. But on my laptop, which I use for work and the occasional arcade game, I don't mess with system files because breaking that system would be horrible. So choose wisely before deciding on what to do. Also, I agree that Defraggler should have a boot-time defrag tool.

To me it just looks like either there is a gap in your MFT space (?), or it's actually defragging your MFT. Even though MFT is specifically made to prevent fragmentation, it happens occasionally. And on those occasions, to the program, it looks the same as a fragged file does. So I wouldn't worry, especially if it didn't damage your system in any way.