Two different links to the same helpful article by Norman Varney here. IMO, the main take-aways:
1. "Couplers are unpredictable, inconsistent, and never neutral. A quality audio isolation device...will perform predictably, consistently, and neutral[ly] in every scenario."
2. "The idea that decoupling ’imprisons’ and coupling ’evacuates’ vibrations is false. Unless the vibration path is broken, or the energy converted, vibrations will be transmitted."
3. "The idea...that rigid mounting of the speaker cabinet to a heavy surface prevents the drivers from being displaced, which keeps phase constant or coherent" is "not likely."
4. "Structurally decoupling removes structural resonances, buzzes and rattles.... When the source of vibration (the loudspeaker) is isolated from the structure, only airborne sound waves from the speakers are heard. From an audiophile POV, dynamic range, low-level detail, tonality, spatiality, etc. are all improved. Everything becomes more articulate because the unwanted influences have been removed.... [Furthermore,] controlling unwanted structural vibrations can mean better-performing electronics. Mechanical vibrations can cause havoc to tubes, digital clocks, laser reading, stylus tracking, electrical contacts, etc."
OK; so why is there any confusion here?
It seems to me the reason, as usual, is that we all have different specific circumstances in our listening rooms. Simple bottom line: if you have a slab (concrete) floor, very little mechanical vibration will resonate from that floor; most of what is transmitted by the speaker will be absorbed. If, however, you have a suspended wood floor, the floor itself becomes a kind of transducer: it will resonate in its own ways as a result of vibrations communicated to it. But your wood floor is not a transducer designed by a speaker manufacturer! Therefore, whatever sounds it produces will not enhance your SQ. So you should try to minimize your floor’s contribution to the overall sound. To do that, use a decoupling device.
FWIW, I’ve tried Isoacoustics Gaias and Townshend podiums. Both excellent products. But what I’m actually using is sorbothane feet that screw into the spike threads on my speakers. Less than $100, and just as effective as either Gaia or Townshend.