Files shrank?
 

I treated my trusty MacBook to a disk upgrade recently, and used SuperDuper to clone the old disk on to the bigger new disk. I just realized that after that copy, the same data that was 70 GB is now only 55 GB. I'm generally pretty happy about that but I'm also curious what magic went on in the copy process that vaporized 15 GB.

Seems like something I might want to do from time to time; I really could not understand why I was using 70 GB to begin with?

Thanks!

It's likely you had a bad folder you didn't know about in /Volumes (due to a copy to a destination device that failed)... generally, the size difference should only be a few GB, depending on how many swap files/temp files/sleep images you've got.