Aluminium Flywheels

So I am wrong. The benefit of an Aluminum flywheel is for an engine with alot of torque, not so much a high H.P. short stroke motor? Does the rotating mass of a heavy Flywheel effect the H.P. like say the difference between a posi unit and a spool, or heavy 11" rear drum brakes vs. rear disc or 10" drums? Steel wheels vs. 2 piece lt. wt. Alum. wheels?