I believe you'll experience the advantage when you attempt to fit a metric wrench on a U.S. nut or a U.S wrench on a metric nut . No trips to the tool box or back to the tool box .
Have you ever had to clean the corrosion from the battery post , screw , nut and cable end ? The C clamp makes it easy . I suppose we could say the advantage of clamps is they serve 2 purposes .