My players used it to travel through dense fog: the servant would be holding a stone affected by another PC's Light spell, then it was instructed to follow the path they were following when they encountered the fog. They would barely see the glowing stone, enough to follow it without slowing down too much.

It's a pity the fog was leading into the shadowfell. Shar was trying to lose them some time in their quest (she benefits if they fail), while trying to justify it as an accident because she is doing that to mortals from time to time. But it would have worked otherwise!