I've done it a few times. If you want specific port adventures, princess gatherings, or spa appointments, they might not be available ahead of time, although you might be able to book on board. You'll likely be assigned 2nd seating for dinner, although can waitlist or try to change to 1st if you like, too. Fish Extender groups are often closed by then. You'll probably get a later port arrival time. Basically anything you would book ahead of time will already be booked by others, but all the other parts of the cruise are just the same. As long as none of that is a deal breaker, it's a great way to go!