[xone]

I don't see a reason to ever shut off the transponder while the plane is moving...why is there a manual switch?

Never been a pilot I'd guess. It is powered by the plane's electrical system, subject to fire, isolate so you have power for other systems.

[rottndog]

It is powered by the plane's electrical system, subject to fire, isolate so you have power for other systems.

I understand that...but...how much power dose a transponder use, and how many shorts/fires have been caused by a transponder? If the engines can broadcast their status themselves independent of pilot actions, it can't be that much of a burden for the plane itself to do so.