Why do people point to an object with their chins?

Not all people do. It is a cultural trait. Most European peoples will point indicating with an outstretched arm and finger.However, I was brought up in East Africa and there people point with a movement of their nose and chin in the direction being indicated. Spanning both cultures, I find both methods obvious and effective. The African method also has the advantage of being possible when you have your hands full carrying something.