They came stock on Broncos and GM pickups and Blazers, and lots of other cars and trucks too, but were used more often through the aftermarket for different reasons than the factory installed them for.
The two most common reasons in my experience were: As a Band-Aid for poor maintenance/alignment/tire condition/poor choice of wheel offset, and for looks.
In the case of looks, just like shocks, if one new one was cool, then three must be better! Besides, that's what the racers would do. Right?
And in addition to just being cool having new shocks under the front end like that, it gave you another place to hang your hot-pink (or add your hot color of choice here) shock boots.
That said, they're good, but not omnipotent at, reducing shock input through from the wheels through the steering system and into your thumbs. Which is, I think anyway, why the O.E.'s installed them in the first place.
Not guaranteed to save your thumbs of course, but every little bit helps.
As their use got more prevalent, people found that they could be used to mask wobbling tires to a certain extent. That got so bad though, that people would start to complain, and want their money back, when adding one didn't solve their poor maintenance practices, even after you told them it wouldn't.
Like rapt0r and chrlsful said though, you don't NEED one to drive your truck. As long as your steering system is well designed, your tires in good shape and your wheels well matched to your tire sizes and axle/suspension layout, and your other systems are functioning properly, you certainly don't need one to drive the truck around. Even at high speed.
I ran without one for years too, on my daily-driver/wheeler, after adding a Con-Fer front skid plate and not liking the way they re-mounted the stabilizer.
But then, I wheel with my thumbs automatically placed outside the steering wheel too.
Paul