Monophoto said:
...but the situation could also present itself with something in nature if the wind is blowing, seascapes with waves breaking, etc.
I voted never. I do rarely take a second exposure if things change like in the above examples, or if the clouds change dramatically, or if fog rolls in, or if the sun comes out, or if 6 wild swans meander into my composition 30 feet from the camera (really happened), or if I think there was camera shake due to wind. These wouldn't really be duplicates, but different images of the same scene.
While hiking I usually follow the trail for a bit, then take big arching loops off into the forest before coming back to the trail. Since I have only 6 film holders, I'd be out of film in no time. That and using a changing bag in the rain while being eaten alive by bugs isn't worth the peace of mind a second negative would give anyways.
Murray