The idea is to get the instrument up off your lap so that the bottom can better resonate and help transmit the sound of the instrument.
Possum Boards are often an after-thought; a flat piece of wood or a couple of sticks that are placed under the instrument when it is played. Papaw's permanent Possum Board is attached to the Dulcimer's bottom and is always there for you.
Each one with . . . "A Voice So Clear It Almost Speaks the Words"