I was in BB and the bar was obstructing a child (maybe 5 years old). The mother didn't stop her from standing up, sitting on her knees, and basically doing anything and everything to see over the bar throughout the show, which, in turn, obstructed my Dad's view.
Honestly one of my biggest pet peeves is the bar rail at theatres that causes the "lean forward" effect. People sitting in the front row with the bar lean forward/ sit forward the whole time causing everyone behind them to do the same.
So to answer your question - the bar appeared to get in a child's way but not an adult (mother maybe 5'2".) but if you're worried about someone blocking your view maybe get AA.