If you've ever used a large file discovery tool like Daisy Disk, you may have stumbled upon a peculiarly large filed dubbed sleepimage.

You now have both the image and the mounted image on the desktop. Feel free to throw your most secret documents into this mounted image. Once it’s copied to the image, delete it from your Mac.

That takes system resources and, for any sufficiently large disk image, also causes older versions of files to get dumped more rapidly to keep newer updates that include the changed disk image.