Decreases Stiffness. Stretching will help you get out of bed in the morning with less stiffness.
Improves Your Mood. Stretching frees up the tissue throughout your body giving you an uplifting attitude for the day.
Improves Back Pain. Since over 90% of the muscles in your body have an influence on your back, the more you stretch the better your back will perform.
Increases Strength Output. If you stretch the opposite muscle group (ie stretch your hamstrings), the strength output of the quads will be bigger since it does not have to fight the tension in your hamstrings.
Prepares the Body for Exercise. When you stretch before you exercise, your body responds quickly. Stretching causes the muscle lengthening to be more efficient and also allows you to perform better.