Except the thermal calibration, all this steps are necessary to achieve assisted modes using the INS13 (GPS Navigation) attitude estimation algorithm, also called EKF (Extended Kalman Filter).
High-quality GPS receivers can provide around 3.5 meters horizontal accuracy. Higher accuracy required for GPS Navigation is attainable by using GPS in combination with augmentation systems. For instance additional inertia sensors. Centimeter accuracy systems such as RTK are not yet supported. Additional inertia sensors such as accelerometer, gyroscope, magnetometer, barometer are absolute minimum of non-redundant information required for navigation.
All sensors calibrated and properly functioning are blended by sensor fusion algorithm (i.e Extended Kalman Filter) to yield a more accurate estimate of a position. Before attempting to use GPS navigation, aircraft must fly perfect with Complementary fusion algorithm, all sensors must be calibrated, functional and giving good data. Although Extended Kalman Filter (EKF) is designed to deal with noise, it can only tolerate certain level of contradicting prediction data. Failure of any inertia sensors in most cases renders whole system not flyable.