Rudi, thanks for fleshing out my answer. The PNR has your entire travel itinerary, all contact numbers registered (home, office, hotel) and other information.

As flight crew this information has proven to be valuable on occasion. Twice in the past year I have been able to return customer passports, left in a seat pocket, by accessing this file to contact them and arrange a delivery to return the passports.

Ozstamps, the locator number just gives information about the present itinerary that you are travelling under when a particular booking is made but the PNR gives information that is permanently kept on your file and can be pulled up every time you book or check in for a flight.