Answer:  If you haven't figured this one out by now through experience, you probably don't need the sweat band on your EWI. Some players, apparently Brecker among them, have the problem of spit running down the under side of the EWI and hitting the octave rollers. If this happens the EWI will only play in its highest octave (as if your thumb was on the top roller) until the spit dries out. The sweat band or pony-tail holder will prevent the spit from running down.