Typically they are on fighting knives, and this randall is a fighting knife. Hence the guard, cause you wouldn't want that feature on a camping knife. It would get in the way for camp chores, etc. A fighting knife feature really.
Plenty of opinions of sub hilts, all that aside just another feature, that some like and some dislike, that helps for grip. I don't know randalls out of my price range, but could be a custom order where the customer wanted it? If its not a standard moldel feature? Just guesses though.