What are all these metal cans/pods sitting on top of electronics?

Don't knock it till' you try it: cryo'd antimatter carefully balanced on top of a Stillpoint- Soundstage will extend beyond your walls and wrap itself around the planet. 

@rushfan71

I use 1 pound bags of cannabis.

Yeah, but the bags keep getting lighter everyday

Speakermarster says it very simple as it is.
my hifibuddies and  myself are using many of these ressonance tweaks and one of my favorites is Ebony blocks about 12x12x6 cm.
by using diffrent materiale and sizes we alter the sound and i sometimes adjust acording to the volumen i play at and the type of recording i am lisining to.

Reading some of the comments make me wonder why some people cannot hear these for me obviously differences when you are damping or undamping the chassis of a component.

Could it be that some systems simple have too many constrictions in the signalflow so you need to find these before you get the bennefit from a more optimised chassis
. I think to observe that  one of the trends in ultra highend is that the chassises have become more and more in focus and clearly better optimised.

One of them could be seen with the step from the Audio Research 40th Anniversary to the Ref 10 preamps where the Ref 10 had so much more focus on the chassis. Both models acted very much when you removed the topplate or when you dampend them with  reconance tweaks.

Its a very cheap tweak but i takes a lot of time to find the right material and the right spot to place them. 
It obviously that diffrent chassis need diffrent tweaks.

By the way i feel the same way with the windows in the lisining room, tweaking the glass ringing makes a clear difference in the sound of the room and thereby the sound of the music.
So another nice challange and never ending story for the audiophile

Seems like a lot of ground has been covered but Mr. Darko also made quick vid on them. https://youtu.be/Dvz2SaHzn3U

None....I repeat None of these tweaks will work unless blessed by the Pope!!!!!!!