Why do we measure elevation relative to sea level? I understand that water settles to a level surface, but why not just measure relative to an ellipsoid and dodge all the sea level rising, geoid, and other problems. I'm looking for a real world example where height relative to a geoid is more useful than height relative to an ellipsoid. What could go wrong if I used height relative to WGS84 ellipsoid for example?
I'm new to all this and thought about it for a day but couldn't figure it out.