Covers on unused RCA inputs?

Years ago, I vaguely remember being advised to put little plastic covers on the unused RCA inputs on the back on my preamp. These plastic plugs had a piece of metal that connected the two poles of the RCA input. The theory was, by bridging the two sides of the RCA input, ambient RFI and static electricity were blocked from entering the preamp, resulting in a lower noise floor.

Of course, these plugs could only be used on RCA inputs, not outputs, as this would short circuit and possibly damage the preamp.

Has anyone heard of these gadgets? Does anyone use them currently? Thank you.