The objective is to center the boot/foot on the board (it does not really matter where the binding is positioned). Some bindings allow for different positions of the boot within the binding/over the baseplate (e.g., by moving the heel loop) to achieve this.
Other bindings do not have that adjustment, so in order to achieve a centered boot/foot you might have to move the entire binding. These disks allow you to do exactly that by mounting the 'channels' perpendicular to the edge of the board.
If you find that your boots are centered already , you can mount the disks with the 'channels' parallel to the edge instead, which will allow you to fine-tune your stance width (almost like ICS/EST).