So instead of having one app to do everything, you would rather configure app after app to do the same job?
I use the mixer a lot, I listen to tunes constantly. I use winamps global hotkeys, but it is so much easier to use the mouse wheel for volume (I currently use the freeware app volumouse). There are also many games/app (e.g. bf2, CSS, windvd) that reset your mixer settings meaning you have to reset them everytime you've used them. A hotkey would save so much work.
Whilst it might not be needed it would certainly make life easier because it would automate so much.