My thoughts are that the early banded horns, with a single band in about the center, had the band to protect against ware. Over time the bands were turned/carved with decoration and more bands were added as decoration. If you look at the Funk horn pics you see a very plain band. Some Pa. horns have a single band, most I have seen have been decorative turneing, at the base as do many Southern horns.
Who really knows whether they were decoration or function?
Tim C.