They are not required as there are other media you can use for the same function.
You could also use an admission/key card, or Magic Mobile via your smartphone/compatible smart watch.
If you have any old Magic Bands assigned to your account, they should still work (if too old, ride photos/long range may not read, but tap functions should). NOTE: if they are already assigned to a person/profile, they cannot be re-assigned to anyone else.
From what I recall they can be used for:
Currently:
Unlock Door (if on property)
Admission Tap In
Room Charge Backs (if staying on Property)
PhotoPass photos
Ride Photos
Rider Swap
DAS
Future:
G+LL/IAS return windows