No, definitely not needed for one day or ten days or every day.
The only thing I would make sure you do is get a KTTW card...the phones have been HORRIBLE at opening the doors. Sometimes they work, sometimes they don't and we ran into probably 4-5 CMs who didnt know what or how to scan the tickets in our wallet for different things throughout our trip.
If you're staying on property and complete your resort check in from your phone and skip the front desk and your phone doesnt work, they do have a number you can call and they will send someone over to let you in but make sure you ask them to bring you a KTTW card. If you do check in at the front desk, just make sure you get one then. if you're not on property, no....don't worry about the magic band at all. Its just one more thing to worry about and they force you to your phony anyway so you know you'll have that no matter what.