Sticky pistons are effectors, they push up to 20 blocks in front of them. The push direction can be set by placing them from different angles. Sticky ones also pull 1 block. A sticky piston pointing into an unloaded block won't extend. A sticky piston retracting from within an unloaded block works and pulls a node, but if it doesn't pull anything, then gravity-sensitive nodes above the empty space may not fall. An extended sticky piston that touches the surface of an unloaded block and loses signal retracts but doesn't pull anything.