I have a course with a lot of embedded videos; I replaced all of the video files with embedded videos from YouTube in the hopes of reducing the size of the course to make sharing easier. About two weeks later I went to make a backup of the course and it was still over 300MB, I would have expected this to be reduced to about 20-30MB total. I can confirm that the cron is running.
I thought that Moodle would delete files that were no longer being used after a set period of time. Files that are no longer used as part of the course should be deleted or removed from the backup.