Across the front and rear wheel, it helps to judge the balance of the car while cornering. Like below my track car is being corner balanced. They use RF/LR is the bench mark. Of course, getting left/right and front as close to 50% as possible. I am sitting in the car with helmet on (hehe)... and the mechanics took this picture
It is near impossible to get LF = RF and LR = RR, mainly because of the design of the car. I doubt even that is achieved in F1???