Stretching can be used as a way to warm up the muscles and it will encourage the flow of blood. This then provides the muscles with an oxygen supply as well as nutrients in order to help them to keep going. You should never stretch cold muscles though. Do some jumping jacks or jog in place to get the blood flowing before stretching.
It Improve Posture
Stretching can also help you to improve your posture and particularly stretching the back. It may also be useful for alleviating pain. Plus, when you stand up tall, it makes you look leaner, which isn't so bad ;-)
When I do stretch more often, I do have less injuries and feel better in general. Careful though, don't over stretch to a point where you cause yourself pain. Stretching should be a gentle pulling of the muscles. If you overextend your muscles, you can cause injury.
Don't forget to breath either. Exhale when you are actively stretching the muscle and you will get a deeper, longer stretch!
Now, I just have to listen to my own advice!
Also, here is a short video with some different stretches to get you going!