You go to the jam, you have no sound check, you have no time to do anything but plug in and tune up. Your amp turns out to be way too bright and there's another guitarist and a bass player between you and your amp controls, you got a tone knob on your axe, you can adapt on the fly without having to screw with your amp much. You turn down a little after your solo, you can roll your tone knob back up to account for the lost brightness from the volume drop. I mean, sure, it's great to have that wide-open, no-load circuit so you can bathe in the coruscating brilliance of your TONE, maaaaan, but it's not exactly a BAD idea to have a tone knob in there. It's practical and in some cases it's good manners. Sometimes the right tool for the job is not Eddie Van Halen's rhythm tone from Runnin' With the Devil.
