Where signal strength is low (in the mountains or a building).

When moving slowly (walking).

When precise coordinates are needed (self driving vehicles).

When precise altitude is needed (airplanes and drones).

When tracking smallish things on a person (head tracking for augmented reality).

When performing certain scientific measurements (continental drift).

Finally, so that when I'm sitting at a stop light my navigation doesn't freak out and suddenly think I'm moving in the opposite direction.

I'm sure there are tons more.