Lighter pistons allow the engine to rev higher. Power = Torque * revs. At 6000rpm a typical piston has to be accelerated from zero to ~50km/h and back to zero

Lighter pistons allow the engine to rev higher. Power = Torque * revs. At 6000rpm a typical piston has to be accelerated from zero to ~50km/h and back to zero 200 times per second. Every bit of weight saving helps.