As there invariably will be something causing earth currents, we have to deal with that in some other manner. Take note of where the mains earth is in all this. The balanced mic inputs on your desk looks at the voltage between pins 2 and 3 for the audio. If their is mains hum that is equal on both pins then the audio recovered will be unaffected. This improves the impedance ballance and is very worth while when there is lots of earth currents or volts about.
Radio signals have to be treated differently as the cable behave as transmission lines.
That is, The current and voltage is not constant along the wire. In most applications or situations what you describe will very nicely suffice for hum elimination. However, we must all keep in mind that exceptions can and do get presented which defies what is nearly always a successful result. What I found was worse than abismal. About 4 years ago we completed construction on a 50k sq.