In the U.S., if you're mailing a large number of items, you can get significant discounts for providing the mail to the post office pre-sorted by the 9-digit ZIP code. To take advantage of that, your address schema would at least need to be able to extract that information.

One compromise would be to impose an address schema by default, but allow users whose addresses are incompatible with it to opt out of it and enter a free-form address.