As far as I know, pinching out the tops of broad beans is recommended if they become infested by black fly. I have never heard of pinching them out to make the beans bushier - I find that mine usually grow more than one stem with no pinching.
As Muff said BB are pinched when near full height to deter blackfly not to get bushy plants this is not a characteristic of BB but they do grow more than one shoot from near the base.