http://vimeo.com/8251405
This is a super-quick video explaining how to assign both a parameter and the device on value to a Marco knob, so that when the parameter is at 0 value, the device is turned off as well.
See Tom Cosm’s site for much Ableton Live goodness.
Good Idea, very useful!
When you use a lowpass, it is maybe even better setting min=127 and max=126. This turns the filter off when the Frequency is at max, so you have a smooth transition.