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

The front end responds more precisely 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 subtler on a modern body that is already rigid.