On a Hobie 16 the boom vang is not necessary unless the boat does not have a main traveler. I think they originally came standard on the boats because so many of them were used for rental boats, and many rental boats did not have a traveler. When you don't have a traveler, the vang helps to control the boom height, especially downwind, making jibing less hazardous and pitchpole less likely.

So if you have a traveler on a Hobie 16, there is no reason to use a boom vang. At least not that I know of. You travel out, and then your mainsheet serves the same purpose as a vang, controlling boom height.