A good 5-10 minute warm up is a must before any workout- be it cardio based or strength training.
Now, a warm up is more than just getting your body "warm", so sitting in a sauna for 5-10 minutes is not the same thing (even though it might feel great!).
A good warm up gets the blood circulating to the exercising muscles, and allows your body to adjust to the increasing demand for oxygen with less stress. By warming up your body you will have greater elasticity in your ligaments and tendons, and you release synovial fluid to lubricate your joints which will prevent injury.
A treadmill, bike, elliptical etc, are great choices for a warm up since they get your heart rate up and blood flowing to the largest muscles in your body. You will want to start slow and gradually increase your speed or resistance until you reach your target zone.
A proper warm up will help you preform better, allowing you to work harder for longer and reach your goals faster!