There has to be a way to shut off or disable just about every piece of avionics in aircraft by the pilots. Sometimes one thing can malfunction thereby affecting another, especially since transponders are hooked to altimeters, thereby normally reading a/c altitude. Though a 777 wouldn't fly out of smaller airports, ATC or ground control usually want you to put the transponder (xdr) in standby mode when taxiing @ smaller airports with approach control since they would have too many transponder returns all piled on top of each other on the controller's screens. That's known as "squawk standby". Larger airports use radar to control ground taxi traffic via radar also, especially in bad weather.