Too much underdrive for a race car is not much of a concern due to the high RPMs they run at, but for daily driven vehicles it can lead to a dead battery if too much time is spent at idle or low RPM.
In the context of race cars, insufficient underdrive is not a significant concern because they typically operate at extremely high RPMs. However, in everyday driving situations, inadequate underdrive can lead to a dead battery if the vehicle spends an extended period idling or running at low RPM.