They say you need to match the runs of power and ground. From what I understand if you only run the ground to the chassis in the rear it has to pass through the entire chassis to get back to the source. So Im guessing its less efficient then simply running it to the front battery. when I finally pull my interior to do my wire runs I think I will also run a few sets of extra speaker wire as well, just in case I want to add something in the future.