A few examples:
Notice all the small stones missing? Others still are holding. These larger stones are 2-3ft in size. I don't know the history of this wall located in Baltimore County on Factory Road. The wall is amazing in size and only one of a kind in the area. Seems a little over the top with all the pinning 90% still in place.
The stone mason uses some stones to help get the lift he needs to the next stone. Other areas he uses the stone to fill the voids. Not all pinning can be avoided.