The thing that pops into my mind is noise adjustment. Like tuning a naval surface radar more or less sensitive to adjust it in calm or high swells.

Maybe it is in real life to wash out the worst noise in a crowded airport like London Hethrow or O'hare in Chicago. I think it will be a lot of other signals that would interfere with the ADF-tuned signal. And on the other end of the scale, the gain could be adjusted different at Bermuda where I guess it is less signal noise.

Or maybe I am totally off course here.