Speed gives you a flatter trajectory which actually improves accuracy which of course is a good thing. As long as you have "excess" energy to do the job that energy will be wasted unless you channel it to velocity where it can be used to flatten the trajectory. Let me exagerate to make the point. Lets say it takes 10 units of energy to pass an arrow through a deer and lets say you have 100 units available. Theoreticaly you could shoot an arrow through 10 deer if they were lined up just right. But wouldn't it make more sense to use say just 20 units for driving the arrow through and the other 80 channel into velocity? You're still sure you can kill the animal but you also are putting the exess energy to good use rather than wasting it.