The barometer gives you better resolution on the Z pos. So it's useful for measuring changes in altitude and the like, provided the weather conditions don't cha

The barometer gives you better resolution on the Z pos. So it's useful for measuring changes in altitude and the like, provided the weather conditions don't change (resulting in a change in atmospheric pressure). Though without some kind of calibration, you can't determine your altitude from the barometer alone. It can also be useful to calibrate when enough GPS satellites are visible, then continue providing the altitude, even when there aren't enough satellites in view.