How can the position of teeth affect function? I almost want to approach that backwards and say, "How can the position of teeth NOT affect function?"
The position of teeth is important for speaking and for enunciating sounds like our S sounds or F sounds.
The incisal edge determines how we enunciate. The incisal edge position dictates where the teeth hit on the lower lip so we can enunciate an F sound properly. If the teeth are too far apart or bumping into each other, you cannot make the F or S sounds properly, like the little kid who's lost his front teeth and wants them for Christmas. The position of the teeth affect not only our speaking, but it affects how we chew.
The position of teeth affects how we swallow and breathe.
The position of the teeth erupt into the mouth in the neutral zone, in the corridor that is dictated by the inward and outward functions of the muscles and the tongue.