In some countries, post office boxes are quite anonymous. And for that reason, some vendors aren't keen to send goods to PO Boxes. But that's not all countries. In Australia, for example, you have to provide all sorts of ID to the post office to be able to get one.
Why PO Boxes?
The fundamental reason that many people use PO Boxes is to have a relatively safe location for their mail to be collected. At so many houses, letter boxes are quite unsafe. And for people living in apartments, the situation is often far, far worse.
Like everyone else, we've been doing a lot more online shopping lately. What has really frustrated me though, are vendors who don't handle address details properly.
I've had many sites who have a rule built into the UI to prevent entering a PO Box for a shipping address. Even though I'd prefer it wasn't that way, I'm OK with that. But then they use the same address validation logic for a billing address.
Please, please, please don't block PO Boxes in billing addresses. That makes no sense.
I've had sites where I want to buy products, and I can't because they won't let me enter my actual billing address (i.e. a PO Box) for the credit card.
At that point, I can't proceed with the purchase.
And identity theft issues
Stealing mail from street letter boxes, etc. is a common cause of identity theft. Yet, I often find that exactly the sorts of suppliers who should be concerned about identity (utility companies, banks, local councils, etc.) often insist on sending mail directly to street addresses. That's not sensible.
Worse, I've seen people move to a new address, and the bank sends details of the change, to their old address ! i.e. the place where they are no longer living. I understand the decision process that led them to do that (in case the move wasn't real) but think what they've just done: 99% of the time, they've sent private bank-related details to an address where someone no longer lives.
Another common situation is where people travel a lot. While that's not an issue for us right now, it is at times. And having mail hanging out of a street letterbox isn't helpful security-wise. We fortunately have good neighbours who will deal with that but the issue is that we shouldn't need them to do that.