Some people simply remove the system because it adds weight and complexity, and is another potential source of issues - specifically:
The pulse air has 'snorkel valves' in the airbox which are controlled by vacuum from the carburetors. When you are riding along at a good clip and 'chop'/release the throttle, the vacuum lines from the carbs should cause the valves to close, cutting off the flow of fresh air into the exhaust stream. It is designed this way because in this state, there will be alot of excess/unburned fuel in the exhaust flow and it air is introduced at that point, alot of backfiring (pop-pop-poppopopopopopopop!!!!) can occur. If the vavles start to stick/bind or a problem with the vacuum lines cause the valves to hang up, a common problem is excessive backfiring anytime you are slowing down for a stop light.
When all is working well though, it does reduce exhaust emissions - depending upon what your states' requirements are for evaluating vehicle emissions on bikes this old, you may want to keep it on there.
