Agreed, but coupling to the floor or shelf with weight is another thing entirely and especially so with components that are not especially beefy. It can make a huge difference in sound quality in a reasonably compact package. A lead brick 2x4x8 inches weighs around 20lbs. They can be placed atop a component and also be placed around the component on the shelf it is sitting on. One thing I noticed is that what are used as footers for the lead brick matters - felt was for me anyway a big no-no - vinyl or silicone self-stick bumpers commonly available in hardware stores were vastly better. Used lead bricks are invariably somewhat beat up and won’t sit "still" unless given footers attached in a triangle pattern on the bottom.
The bricks should be painted to inhibit oxidized lead from eventually entering the room atmosphere even though lead takes quite awhile to oxidize in the controlled atmosphere of a home. Painting is also helpful to keep lead off your skin when handling the bricks although all the bricks I have purchased are not super soft lead. They contain alloys like antimony to harden them up a bit and not be very "marking" or oxidizing.
I also use these bricks atop speakers to give them more mass, and this had made quite the sonic difference as well although some may object on aesthetic grounds. Painting the bricks black and arranging them in suggestive patterns atop my Cornwall 4's always elicits curiosity and novelty among the guests.