The CG-Lock gives you about 80% of the holding power of a full race harness.

Why do people use a harness?
You don't need to "hang on" when driving hard...you can keep your feet light on the pedals and your hands light on the wheel for better driving control, faster reactions, and less fatigue.
You are "one with the vehicle"...you can sense the vehicle movement better, react sooner, and "feel" your way through the tricky spots more easily.
Your safety is increased.

Unfortunately, most of us do our autocrossing in our daily drivers with standard three-point automotive seat belts, not racing harnesses. Once the CG-Lock is installed, you pull up on the shoulder harness of your seatblet, and the lap belt portion gets "racing harness tight" and stays as tight as you want until you release it!
Simple, But what a difference it makes.

Improves the performance of the DRIVER, not the car! Your hips are your body's center of gravity. Tightly help hips provide the first two of the three benefits of a full harness as described above. As for the 3rd benefit-increased safety- the CG-Lock is not sold as a safety device, but it has been designed and fully tested to not interfere with a seat belt's safety.