Some science behind the scenes
The chin is a trigger point. This is best seen by looking at the course of the nerves which the energy flows parallel. In the diagram below you can see that there is a cluster of nerves on the chin. By pressing the chin here one is, in effect , triggering the nerves in this area.
Energy from the chin meets up with all the other energy from points on the face and follows the course of the trigeminal nerve which you can see in the diagram to the left.
You can also see why pressing the cheek, the top lip and nose sides also affects the trigeminal nerve here.
The mandibular nerve (V3) carries sensory information from the lower lip, the lower teeth and gums, the chin and jaw (except the angle of the jaw), parts of the external ear, and parts of the meninges.