When I came up with the list I was considering your initial question about a directional microphone and
"why distinguish between voices and background noise?" So some of my examples were not restricted to directional microphones only. Given the new constraints:
Factory workers: Increase awareness about the sounds of the machinery the worker is operating and ignore the sounds of nearby machines. In a more hostile/mobile environment where the worker does not need to be so in tune with their own machine the directional microphone could provide the same benefit as it does with construction workers.
Construction workers: amplify noises from directions where the worker is not looking and therefore increase awareness of threats from blind spots.
Bird watching in the amazon: Isolate/focus scientists hearing in the direction of the bird that they are observing. Thereby reducing the possibility that they attribute sounds/songs from other birds to the bird they are observing.
News camera man: increase ability to hear sounds in front of camera man and/or directions from reporter/crew members while reducing distraction of environmental sounds.
Why are you moving the goal posts?
