This is cases when your Y is like 5,000 studs. At those heights, other players (not yours) will appear more in the ground, and this is per client, because the other players will see they are taller and others are not.
Due to the fact that parts are deleted at Y=-500, and you want to have a game that goes far down (ex: The Quarry for example, or Innovation Security’s pit of death where the training facility), you need to make the altitude super high.