Some also change the power line impedance in a way which is supposed to be better. We will leave it to your ears to decide if these devices help the sound of your system enough to justify their expense. Some complain that heavy foot falls will cause skipping or more subtle sonic problems with CD players or turntables. If you have these problems, there are a few different things which you can try to reduce the problem. One is to add weight to the rack which holds the equipment.
Heavier things move slower.
If you can get the motion slow enough, it won't cause sonic or tracking problems. This might make it better, but might also make it worse. A third solution is to increase the coupling between the rack and the floor using spikes, which concentrate the weight on a very small area. Another way to increase the coupling between the rack and the floor is to use a plastic adhesive like HoldIt, sold under the UHU trade name in office supply stores. Unfortunately, these systems are usually the high-end ones.