This may sound an odd idea, but offer an option to write zeros to all the free space on the volume. i.e. prehaps create a 1MB file full of zeros and then move it across the free space
Why? well some storage arrays detect all zero writes and use them to deallocated the space from a thinly provisioned drive, thus you allow the storage array to know there is no longer any data in those blocks
the theory may be nice, but if by storage arrays, you refer to SSD's, then I think you hit the old brick wall, "limit excessive writes to a SSD".
plus i don't think it would be in the scope of a defrag program to do that, more of a cleaner program, say CCleaner.
SSD may be faster, but seeing all these limitations makes me glad I have HDD.
I can boot cold turkey on my standard sata HDD & be in a usable windows desktop in less than half a minute.
Do I really need to shave 15 extra seconds off boot, since applications run in RAM once loaded anyway?
AND, I can defrag my HDD. Hooray!!!
SSD's have limitations like avoid excess I/O's if you can just like HDD's have limitations like keep away from magnets and don't knock them
Neither technology is perfect, each has their pros and cons.
For some the blindingly fast access times far outstrips the negatives.
But as far as this thread goes, it is a widely accepted idea that SSD's simply have no benefit from a defrag, and the suggestion to include a wipe facility in Defraggler is already in CCleaner.
If the Piriform team thinks this, or any idea, has merit, watch for it in a future release.