Wilhannes is right. It is there just to give you (it comes only with the premium package) some ambient light at night in order you to see your interior.

In order to better see what it does, put your thumb on it and remove it. It may be small and doesn't lit that much when you look at it, but it brings some useful light from what I read.

In my opinion, they should have lit up the windows button first before putting this small led over there.

By the way, should not this led be the same colour as the dash ones, orange?