This has probably been posted here before, but I heard an interesting tidbit from a fellow enthusiast about the purpose of the barbers notch.
He mentioned that the notch was to allow better shaving of the nostril area!! The notch would allow the blade edge better access to the area right below (an inside) the nostrils in order to get those delicate whiskers more easily and with less chance of also slicing something else off.
Interesting....;)