An X pipe nearly doubles the size of the exhaust system from the engines point of view so back pressure drops considerably. The engine exhaust noise mellows out as the high frequency tinny noises are tuned out of the exhaust by way of pulse cancellation. Makes the motor sound bigger in my opinion. It is very beneficial.
I would be sure to include about 18 inches of flex pipe per side (woven stainless steel hose with a smooth interior) if you are thinking of tying it all together. This will allow you to bolt it to the frame and it further reduces rattles and squeaks (but that flex hose is incredibly expensive).