Dave, I don't post this to disagree with Whiteroom, because it's a safe bet that he/she has more experience! But I recently got a pair of Marker pistons that does have the on/off switch, had exactly the same question, and did some searching for answers on this forum. I'm guessing I will leave ON, for the very reason WR gives.... but here is a previous thread where others give their perspectives, including some that seem to like it off for selected conditions:
Originally Posted by dwoof2
I have the Marker bindings with the comshock piston and the on/off switch on front of the binding. I know what the switch does, but not really sure when they should be set on and off. Any help appreciated.
I do ski groomers, powder and bumps.