It's not just crashes that they are needed though.
Mine came in handy when the engine in mine went deadstick (as it was still new, and not run in), and I had to land in the crops to save it, as I didn't have enough height to get back.
But yes, hearing it in a cornfield is near impossible unless you are within about 10-15 feet of it, and if your battery is disconneted you are stuffed, but overall, it could help you out to retrieve your model that may otherwise be lost for good.