You know how Spec grade have the screw terminals that "float" loosely until wired. I have a lot of fun getting 12 gauge wire around those screws as the bob and weave like Sugar Ray Leonard. I wondered why are they made that way. All I could come up with is that if someone neglected to tighten the unused pair of terminals, it would be less likely for them to come in contact with the sides of a metal box.
That's my guess. I'd enjoy struggling with those things a little more if I understood the reasoning.