I tried going without one but went back. I use it for volume of my RH voices. No matter how much I edited at home when I got on the job the voulme levels always seemed to need adjustment. I hate trying to make adjustments while playing/singing. Using the volume pedals also helps add a bit more expression to the sounds.
Like Bernie I was a Hammond guy and used the volume pedal all the time. Right foot volume or sustain pedal for the Rhodes on top of the B3 and Left foot on the bass pedals.