[rotorwrench]

The heavier flywheel allows for lower rpm in operation. Low rpm engines have less problems with higher harmonics. Counterweights allow for a wider rpm band and reduce the need for a heavy flywheel. Ford had counterweights on the model B for 1932 but they still had a vibration damper on the firewall to reduce the chance of vibration resonance.

Opposed aircraft piston engines have all sorts of counterweight configurations depending on the rpm and power application that is is designed for. Some have a large heavy prop and some have a lighter prop. Then there are helicopter engines that have almost no flywheel at all. It's basically only a cooling fan with a starter ring on it. The rotor system is the flywheel on most of them and they are easy to over speed during start up. If they over speed with too high an rpm, it can stretch the connecting rod and lead to crank pin or con rod failure.