It bothers me to walk into a nice bathroom and see a randomly placed exhaust grille on the ceiling or wall. In a small room full of fixtures and accessories, a sense of visual order is important—and a haphazardly positioned grille shouts for attention. Thoughtfully placed ventilation, on the other hand, is virtually invisible.
Of course, aesthetics is not the only consideration in positioning bathroom vents. Exhaust grilles perform best when located high on the wall or in the ceiling and as close as possible to the source of water vapor (over a shower, for example). Proper installation of the system is also essential.