What is the benefit of the OPN?

You can not only see the product and its attributes as you can in the salesname but also information about the RoHS status, the halogen status, the totally lead free status, the functional packing type and size as well as the moisture protection packing. You can also distinguish other product variants based on the designator.
The descriptive nature of the OPN and its order relevant level makes it easier to communicate: Talking about SP numbers is not convenient as they are simply numbers. Talking about Salesnames is not sufficient because one salesname can have several ordering codes.