Which component(s) benifit the most from isolation?

I think one's goal should figuring out how to decouple in a smart way.

Pretty much everything in two systems use HRS isolation products , some come from factory w HRS built in ( Aesthetix ) but as a slaw mentioned above there are less costly methods notably springs and a seismic sink ( sand )’or even a combination including added mass… 

The problem for years, has been the word ’isolation’ thrown around as a general term that throws a wide swath....In our world.

"Anything with tubes" sounds right to me. Also, tape deck if you have one.

I have an isolation device called Pontoons, special plastic horizontal cylinders with supporting cups(3 per item). I began with a CD drive(I have an external DAC) and the change(for the better) was as if I bought another, better, CD drive for much more money. I also have the devices under my line stage, phono amp and amp and always noticed easily a difference I thought was better but nothing like the initial use under my CD drive.