If you do online check-in, and you have a magic band, you should get a text or email with your room number, so in theory, you should not have to go be the Great Ceremonial House. In practice, it is smart to go by checkin at the GCH if you want to use your Magic Band to charge purchases during your stay. I had pre-registered my credit card during online check-in, but I discovered that this did not necessarily mean that I could charge things with my Magic Band. I could only do that by registering the card at the front desk. Also, sometimes the Magic Bands don't work. You can test this at the front desk and save yourself some frustration. I love Disney, but their computer systems are their Achilles Heel.