It will go through and remove the “Quarantine” flag on each file (whether it has it or not) which should allow the screen saver to bypass Gatekeeper and be opened normally.
(n.b. Technically you don’t need the -print part, but otherwise it won’t show anything as it works, which can make some people wonder if it’s doing anything. With -print it will show each filename as it is processed, giving you something like a progress indicator.)