The limbs cancel each other out in the shock department. The theory is that they move directly away from each other. Non parallel bows the limbs move away from the archer, both at the same time, creating the feeling that the bow is gonna "jump" out of your hands. The parallel limbs move straight up and down both equally opposite of each other. They are also said to be quieter as well, but I am YET to hear a bow as quiet as my UltraTec.