What is a set piece?
Select any prop in your set and you can make it a set piece. As you add shots to your scene, this set piece will remain in the same location throughout your scene. If you move any set piece, it moves throughout each and every shot in the set.
For example, suppose you have a BEER BOTTLE on top of a RESTAURANT TABLE. You want to move the BEER BOTTLE to get a better shot of your actor. If your scene has several shots, you can designate the BEER BOTTLE as a set piece; move it once; and the BEER BOTTLE moves in every shot in your scene.