Gets the blood pumping to your muscles and increases blood flow throughout the entire body.
What happens if you take a dry sponge and pull on both ends as hard as you can? Now pick up the pieces that fell on the floor from that sponge and throw them away. Get you another one and soak it with water and pull again. Obviously with enough pulling they will both tear in half, but the wet one will hold up better to the tension.
Or...
Hop in your car on a cold day and drive it as fast and as hard as you can without letting it warm up for a short time?
Pick your analogy!
Stretching a long with proper 5-7 minute cardio warm up plays a big role in preventing damage, as well as building muscles.