I believe that Garmin provides alternate power inputs so that you could wire the GNS430W to a separate power switch. The benefit would be that you could energize the GPS/NAV/COM and program a route, listen to ATIS, perhaps get a clearance all with out draining your battery with the master on and whatever might run with it.
Beneficial for some, not so much for others. It all depends on what your wants/need.
Don