the sun...my buddy has one in his 1.8t

 

What he said. This blocks the sun that otherwise comes through the gap between the 2 large sun visors.
It is that kind of details that makes an Audi an Audi!

 

It works for the sun, but really it's to keep the glare from the reading lights off the mirror when they're used at night. In an old civic I used to tape off part of the reading light to reduce glare, but Audi has conveniently provided a fix for the issue.

 

There is also the coat hanger hook that comes out slowly instead of jumping out that makes and Audi and Audi...