I had the problem of losing 8 GB of space after using defragger. Searched many"expert" sites for a remedy none had an answer. I came to the conclusion they all had read the same book.I found the solution for myself and gained even more space than before This solution will shock you in a nice way I hope. Its quite simple. Open CCleaner , run Analyze and clean then go to tools and select Disc wipe, this will wipe free space and should return the missing GBs. In my case I RECOVERED 11GBs and a considerably faster machine.
Hope this works for you.