Running a H Pipe,whats the advantage

It quiets the exh in addition to helping to even out the pulses in the headers side to side. But, the way to do it is to put it (or the X) in the right spot... Which in most cars is not possible. I dont you'd see a huge increase, but it might help noticably. The X is a better design, but again, they can only do so much that far back.