Like Bill said, in case of a plow, but also in case of a winch, which was also a factory option back then. PTO even!
Just like the flip-up-down(?) rear plate bracket. So you could run with the tailgate down and still have a visible plate.
And the side brackets for holding the swing-away tire carriers over to the passenger side fender, in case you were running with the gate down for either longer cargo loads or while using the big auger thingy that a lot of them had.
Pretty good thinking on Ford's part at that time I'd say. Figured they'd be selling some to the utility companies and farmers and such, so gave it a few extra perks.
Paul