Well there's a few reasons for having a harmonic balancer.. It helps smooth the vibrations on the "free" end of the crank making it easier for the bearings to keep the crank in place. It helps absorb the shock from the engine going under load and unloading. Helps reduce vibrations transferred to the belts and other pulley's. In theory some think running an undampered pulley will cause premature wear on the bearings and cause crankwalk.