In very rural areas, the USPS has no delivery to individual homes/streets, and only offers post office boxes to residents. This makes perfect sense, and is not the issue. The problem is that it's not possible to associate a street address with that box.
If one is receiving a package from another carrier (i.e. UPS or Fedex), one must make sure the street address is used. If one is receiving a package from the USPS, one must use a PO Box address. This is annoying because it's not always known what carrier will be used, and explaining this issue to others (i.e. family) over and over gets very old, very fast. If the wrong address is accidently used, the package gets returned to the sender.
Please, for those of us in this situation, let us associate street addresses with our PO boxes.