Squeak..... get an expression pedal - it's FAR more versatile. You can chose which parts are affected, and which aren't, and usually by how much, and even sometimes you can reverse the effect and create a cross fade effect.

As to controlling an entire rig, I wouldn't want to put that under the control of a footpedal. Too easy to accidentally hit it and either disappear or blast your audience out! Adjustments to overall volume are easier dealt with at the mixer (which, hopefully, you keep close by!), or by the volume knob of your arranger.

Beware too much at your feet! Especially critical functions that can kill or damage a song....... I don't mind sustains, variation changes and fills, leslie control, Break/Mutes at my feet, but I am wary of things like Stop/Start near my feet (which I may not be able to see well, while I perform!

An overall volume control using a volume pedal (as opposed to an expression pedal, which can alter lead sounds without killing the arranger side) is difficult to use for very small changes in volume, but FAR too easy to overdo.