I have it on good authority that this is why the headstock was invented:
Let's say you really need to go somewhere, and you're up a creek without a paddle. You have a canoe. Fortunately, you also have a guitar!
Equally fortunately, when using a guitar as a canoe paddle, the headstock acts as kind of a handle/stop to keep the guitar/paddle from slipping out of your hands.
Or, imagine that you're under attack and have to dig a trench for cover, but you don't have a shovel, you only have your guitar. Do not despair! A guitar can make an excellent shovel in an emergency! And of course, the headstock once again makes for a handle and stop to keep the guitar in your hands while you're frantically digging.
It also makes a nice swinging weapon, a very dull axe, and a way to defend yourself against your wife's rolling pin.
Even tennis rackets and baseball bats have handles or a ridge at the base designed to keep the thing in your hand. It would be a calamity to be in the middle of a match or game, swing a guitar you're using as a racquet or bat, have it fly out of your hands, and cause lethal injury to your teammate or partner.
Back when I had a Steinberger in the studio, I used to worry that one of these emergencies could easily arise, and I'd be stuck with no way out of a significant dilemma. Needless to say, as soon as the worry became serious enough, I replaced it with a guitar with a headstock!
Yeah, a headstock is a pretty good and useful device. Thank goodness the Great Gods Of Guitars came up with the idea!
Important caveat:
Hanging a guitar on a wall or stand by its headstock is not, repeat, not a legit use of a headstock. 
You knew I was going to get around to that, right?
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