Minecraft wiki entry for Piston, associated text: Longer vertical extenders require complex circuitry, and are often used as elevators. To slightly simplify the required circuits, a gravity-affected block like gravel or sand can be used as the elevator platform. This avoids the need for the top piston to be sticky and for it to execute multiple extensions to pull down the top block at each stage of descent. If more than two pistons are used in total, multiple extensions of lower sticky pistons are still required to pull down the pistons higher in the stack, which are not gravity-affected.