I think the answer to question 1 is directional control. If the left system is u/s then only the right reverser is available and it is also posible that there is no nose wheel steering (if there has been a complete lose of fluid) therefore differential braking would be required. sayin that though I do remember a TC mumbling something about loss of the left system pressure and the possibility of not getting truck tilt so therefore no autobrakes but i'm still trying to figure that one out.