It mattered a lot for me when I was still uisng turntables. I couldn't bring my volume any higher as it would send LF feedback from the turntable when playing. I corrected this using marble slabs where the turntable sits plus expensive isolation footing for the turntable.
Even cassette tape players are said to be adversely affected by surface and air-borne vibes. I am not so sure about amps, though I came across an article that says power transformers and filter caps are adversely affected also.
With CDs, there is a case made in favor of these isolation devices. Some flimsy cd transport shells are so light some vibration coming directly from the solid surfaces the player sits on or air-borne vibes (called microphonics) can induce disturbances on the CD transport mechanism to compromise laser pick-up. Especially when playing at loud volumes. And we all know what happens when we knock or rock a CD player. Appart from skipping, digital jitter is said to result likewise.
The digital age somehow made those isolation devices less compelling. Just the same, I think it's simply a good practice to use sturdy, heavy and robust shelves on which the components sit and to use well-built components to begin with.
For sure, you do not want to place a CD player on top of a speaker.
But i won't go so far as to place a marble slab over a CD player.
If you can afford those isolation devices that are demonstrably effective, why not. But I think there are simpler and cheaper ways to achieve their objectives. I've mentioned a few above.
