The brace connects the two shock absorber top mounts. In a hard corner, the loaded side of the suspension pushes outward and the geometry deteriorates at the exact moment you need it most: the brace distributes the load between both sides.

The front end becomes more precise when turning in, and the car maintains the same response from one corner to the next. The effect is clear on older chassis, convertibles, and high-mileage cars; it is more subtle on a modern body that is already rigid.