Vibration - What are the Main Sources?

The goal is to isolate the speakers from interacting with the floor. When that happens the vibrating floor essentially becomes part of the speaker typically resulting in muddy bass and obscured midrange and detail. Suspended plywood floors found commonly in modern homes in particular are problematic in this way.
Springs under the speakers might work fine though they do not provide a firm foundation for the speakers to operate on. Might produce some interesting results but have never tried. I personally use isolation pads and stands, not springs. I do have some spring loaded feet under my dac but don’t think they are critical for that.

Yes everything vibrates. But some will gladly play others by stoking fear and uncertainty. Including fear that some undetected vibration will negatively impact some audiophile’s sound. Once a fear of some problem exists you can then sell some expensive esoteric fix that nobody would care about otherwise. It’s how these things work. Marketing is all a game you know.

For isolation from EM fields Start with physical distance between components. Especially keep preamps and source devices well away from power amps and powerful amps from each other. Also from any nearby appliances with transformers as well if possible.
Low level phono amps are most sensitive. For example I placed my step up transformer in a mu metal foil tube to shield it from noise induced by nearby electrical devices.

Avoid running power wires parallel to each other and ICs if possible.
For physical isolation isolate speakers from floors if needed as in case of suspended plywood floors. If things in the room vibrate when you jump up and down speaker interaction with the floor is a likely issue.
Turntables are a whole other story when it comes to physical isolation.
If you address these things in most cases should be on very good shape. If gear rests on any solid foundation to start additional physical isolation will likely not add much if anything.

The main source of physical vibration is the speakers which can interact with certain floor types and muddy the sound. Also can cause noise and distortion to be picked up by turntables in particular.
The other important form of Isolation I have found is  isolation from Electromagnetic fields created by transformers both in amps and in nearby appliances, wires,  and digital gear/circuits in general.