In the UK a PO Box is also an address, which you can use in different ways

Mail addressed to the PO Box -> You collect from post office

Mail addressed to the PO Box -> They deliver to street address (which only they know)

Mail addressed to street address -> You collect from post office

The most annoying thing I found was that they would only let you have a PO Box in a town if you had a street address there, which I did not.