Scaling an item (prop or figure)to 0% makes little sense (the item is still in your scene and is still using memory). If something isn't of use, just remove it (either through the menus or by hitting the Delete key). The difference between props and figure is that props are not posable (ie. there are no moving parts). If your item doesn't need to have moving parts, its best to make it a prop. Also, Props can be be made to link automatically yo a set position on a figure (smart props). Figures have to be made to conform to react in the same way (and parenting and conforming isn't the same thing either).