I live in a place with complicated shipping. My street address doesn't get postal mail, so I have a PO box for that. This has taught me some things I never knew.
1 - Lots of places don't take PO boxes, and also won't take the special address format the post office recommends when shipping methods are uncertain. This leaves me in shipping limbo a lot, and packages go missing.
2 - UPS will ship to our house or to our PO box. However, they may send some things via USPS instead, with no way to predict when it will happen, meaning items addressed to our house go into limbo.
3 - FedEx will apparently not deliver (or not reliably deliver) to a PO box, so if we give the PO box and they ship FedEx, the package goes into limbo.
"Limbo" here means, invariably, that our crappy post office sends things back to the sender. This was never a problem when we had a private post office, but it's been an official post office for a year, and since then it has sucked.