And more leverage. That's why many of the super car brake systems have less piston area than the single piston caliper that came from the factory.
Additionally, most multi-piston calipers (depending on design and material) are substantially stiffer and weigh less. A great example would be when Mopar Action ran a first gen Viper caliper on one side of a car and a stock single piston caliper on the other side. The car stopped straight and they saw no pull when the brakes where hammered. The Viper caliper had less piston area, and thus didn't have the clamping force of the stock caliper, but because of flex in the stock caliper they both exerted the same clamping force on the rotor.