Vehicles with a leaf spring and shackle set up lean heavily on the springs to take the shock out of a bump. Not only does a leaf spring reduce the force of a bump that you feel, but it also evenly distributes the load across the chassis instead of the whole load pressing down on one point. Your ability to get to point A to point B without scraping the pavement is heavily dependent on the leaf spring and shackle bushings which mount the spring to the frame.