Which component uses less brake pedal effort with more effectiveness?

The use of a Vacuum Booster is essential in modern braking systems as it amplifies the force applied to the brake pedal, making it easier for the driver to stop the vehicle with minimal effort. The vacuum booster utilizes engine vacuum to increase the force exerted on the brakes, allowing for greater braking effectiveness without requiring significantly more effort from the driver. This is particularly beneficial in vehicles where reducing driver fatigue and enhancing braking performance are priorities.

In contrast, the other components listed serve different functions in the braking system. A Power Booster, while similar to a vacuum booster, generally refers to systems that may use hydraulic pressure instead of vacuum; its effectiveness can vary based on the vehicle's design and is not universally more effective with less pedal effort. A Return Spring is designed to return the brake pedal to its rest position after being pressed, but it does not contribute to the force amplification needed for effective braking. Lastly, the Spool Valve is a component related to directing fluid in hydraulic brake systems, but it does not enhance pedal effort or braking effectiveness directly. Hence, the Vacuum Booster is specifically noted for its role in reducing pedal effort while maximizing braking capability.