But the box might also have flaps or "doors" that you break open on one end to allow the wire to pass through. You can break out one side of these flaps (instead of punching them all the way out), creating a kind of "door" that will act as a clamp to hold the wire inside the box.
No, don't need to use the "clamp method." Electrical code only requires that you staple within eight inches. And you may find those flaps to be more of an annoyance than anything.