Exercising on one leg is important because it helps to:

1. Improve balance and stability: Single-leg exercises challenge your balance and stability, which helps to improve your overall control and stability, especially when running or jumping.

2. Strengthen the hips and legs: Single-leg exercises target the muscles in the hips, legs, and core, helping to build strength and stability in these areas.

3. Reduce the risk of injury: Strong hips and legs can help reduce the risk of injury, especially in the knee and ankle joints, by improving overall biomechanics and stability.

4. Enhance performance: Improved balance, stability, and hip and leg strength can help enhance your performance in running and other activities.

5. Address muscle imbalances: Performing exercises on one leg helps to address any imbalances in strength and flexibility between the two legs, helping to prevent injury and improve overall performance.

It's important to include single-leg exercises as part of a well-rounded workout routine to improve overall fitness and help prevent injury. Start with lighter weights and gradually increase resistance as you get stronger.