I tried to come up with a good reason to have one here is the closest reason that might make sense for someone to have it.
The one use I could think of is it could be great for an instructor at the track if they could find a way to mount it and not interfere with the mounting of a steering damper as this could be a safety issue.
But then again looking down anytime you are on a bike is never a good idea but it could be better than having to turn around on your bike and look back as an instructor. I also see a problem with trying to see the LCD display when it is bright outside. It's like trying to look at your cell phone on a sunny day and not being able to see anything on the screen which would be like riding without mirrrors anyways.