morst, the fact is that when this technology was developed in the 1970s, it was before the great proliferation of consumer devices operating in the GHz range. Nowadays in any venue where you or I record, there is likely to be quite a number UHF transmitters near our microphones. This was not the case back in the 70s.
(As I've mentioned in another thread, I'm currently listening to the complete set of sessions from this past October's Audio Engineering Society convention--and at least a dozen of these recordings contain perfectly audible pickup of Blackberry signals. A random instance that I just came across is attached.)
The upshot is that in situations with severe electromagnetic interference, it is indeed best to have balanced signal sources--and above all, balanced inputs in the devices to which those sources are connected. That is simply a better arrangement technically.
Best of all is when the connections from the cable shield to the chassis of the equipment on both ends is absolutely as short and direct as possible--unfortunately in low-cost portable equipment, this last point is often overlooked, making the equipment far more vulnerable to interference than it would otherwise need to be. Sorry to say, much "conventional wisdom" about shielding and grounding is seriously outdated by now or in some cases, was never right to begin with.
--best regards