What's the point of the usual "please keep your seat belt fastened until the aircraft stops completely (at the gate)" in large passenger aircrafts? Since the plane is on the ground, it is not moving very quick. Even if it stopped abruptly, the seat belt won't prevent me from banging my head against the seat in front of me since it's a two-point seat belt.
The only reason I can think of is if two aircraft collided with each other, which could potentially generate enough force for the seat belt to be useful. Though, I could argue that when a plane is taxiing to the gate, it has to abide to a certain speed limit, which would render any kind of collision not serious enough to be prevented by two-point seat belts.