Savageduck
A non-destructive workflow makes that irreversible function very reversible indeed.

Once that working copy has had USM applied, the layers merged, and compressed into a JPEG (a destructive action) then Floyd is correct, the function can no longer be reversed. However, Floyd doesn't see the concept of the non-destructive workflow because he doesn't, or appears not to use one. He certainly isn't using what is available to those running either Lightroom or Photoshop CS6/CC/CC 2014, and ignores that some here have the ability to take advantage of a non-destructive, or "reversible" workflow because of the software tools installed on their computers.