the idea is an option for shapebox's vertices that makes them magnetic(while using edit corners mode)
it's just what the name implies, dragging one near of another one will move it right along side of it's position.
it can be really useful while working on big models that has high amount of shapeboxes, ton of time can be saved.
the second one is a variant of shapeboxes that don't deform textures, in a similar fashon of those shapes.
With those shapeboxes you can pull full shaded models like this one: