It's all about reducing transmission of cabinet resonance from the speaker to the floor. This way you hear the vibrations of the driver, not the vibrations of your floor. Energy transferred from the speaker cabinet to the floor effectively turns the floor into one large transducer and, as you can imagine, a floor doesn't make a very good speaker driver. If a perfect speaker cabinet with no resonance could be designed, then there would be absolutely no benefit to putting that speaker on spikes. Unfortunately, no such perfect speaker cabinet exists, so we put spikes under our speakers to cut down on the transfer of vibrational energy to the floor. Incidentally, this is de-coupling...not coupling. Spikes do not, nor ever have coupled a speaker to the floor in an acoustic sense. Yes, they do anchor a speaker in the physical sense, but that has nothing to do with acoustic coupling. This will start a war, but I'm tired of hearing it wrong. Acoustic coupling refers to efforts to maximize vibrational energy transfer. To do it with a speaker, you would remove the spikes and put weights on top. Try it and see how that sounds. Then try de-coupling with spikes...you'll never want to be without them again.