What are the circular discs people use on components?

Most people use the door stoppers not for any "resonance" damping, but merely (as John Darko showed in many of his YouTube videos from two years ago) to hold lightweight components like streamers and DACs in place such that the weight of the cables doesn't pull them off the shelf or hold them up at a flaky angle.  Yeah, the weight would likely lower the frequency of any resonances, but your mileage may vary on that. They are a cheap fix and don't look that bad. 

Interesting for sure. Does anyone have any advice as to the amount of weight one should use? I assume it’s more for heavy amplifiers and less for lighter components  

If you've got circular ring above your component, then you're probably not in this world anymore.

I hope the people who buy these remember to check the blinker fluid in their cars.