They help keep the a/c maneuverable especially in yaw (Rudder) and to maintain elevator effectiveness at very low speeds, let alone during stall and spin, due to their oversized surfaces to counter diminished airflow over them, with the addition of propwash which however raises the issue of torque, P factor, and gyroscopics effects.
Inverted oil/fuel sytems keep positive lubrication and engine from quitting at extreme attitudes/during prolonged spin, or inadvertent inverted flight entry.