I'm using some JM Labs speakers right now. They weight 28 kilos each and are quite tall. On the base are four rubber feet. They also come with spikes that screw into sockets in the middle of the rubber feet.
So the idea is that if you have a wooden/laminate floor you don't fit the spikes, so as not to damage the floor, but if you have carpet you fit the spikes to pierce through the carpet and 'couple' with the floorboards or concrete beneath.
But if you have carpet plus underlay (not just a rug) under the speakers is it not best to let them just sit on that, on the rubber feet? This way they are decoupled at least to a degree, from putting vibration into the floor. With the spikes you deliberately connect with the floor and so increase the amount of vibration transferred. Even a concrete slab will transmit vibration. Worse for wood. So the provision of spikes for carpeted floors makes no sense. Hence spikes make no sense. They are just a sub-optimal way of getting, as Jerry puts it, a 'bit of air' under the speaker. Which I agree is a good thing.
Current Lash Up:
TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.