Take an alignment rod (or one of those sticks they sell in the hardware store to mark your driveway before the snowplow comes) and place it firmly under your left armpit. Get into your normal address position, and turn back as if you were making a backswing. Now turn through as fast as you can. Not much speed there. Next, hold the rod with your normal grip and whip it through using your hands and arms. Not only will you see the difference, you'll hear it. And the more relaxed you keep your hands and arms, the faster you can swing the rod. The same is true for your golf club. Tension destroys speed.