Imagine you are standing on a ladder six feet in the air replacing a light fixture. In one hand, you are supporting the weight of the fixture as you align it with the electric box. In the other hand, you are precariously balancing the mounting screw with a cruciform drive on the bit of a screwdriver. As you gingerly raise the screwdriver to the mounting hole, the tip grazes the edge of the fixture. The screw plummets to the floor. Now you are in a predicament. You cannot let go of the light fixture to retrieve the fallen screw, but it is too far below to reach without dismounting the ladder.
Such an occurrence is an ordinary setback to a handyman. In a high-volume assembly operation, however, regular or intermittent dropping of screws during installation can be catastrophic. To prevent that from happening, manufacturers often employ sophisticated methods to guarantee that screws with an internal drive recess are delivered to the assembly point and successfully driven every time.