The intersections of the two axes indicate the clamping forces at various speeds. You can put counterweight on and take static load off, for example, and then you can put real numbers to that combination. Without this information, all changes are based on experience. It's not revolutionary, it's only another tool. It does not automatically mean a team is going to pick up a lot.
All racers have baselines, but when or if they desire to make changes, they can be done on the dyno.
It confirms the direction and the magnitude of the changes. You can learn from testing what would take years of running a car. Each clutch is tested without its discs and floaters. They are replaced by a load cell. It also is called a strain gauge, which is used widely in industrial applications and other types of dynamometers.