I remember from the owners manual of my E36 about 20 years ago it stated the reason for having this was so that you could blow cool air to the face to help keep you more alert, without making the ambient temp too cool for everyone else. It works very well at that.
I use this feature all the time on my M3 (and all my past BMWs) but really miss it when driving my wife's Audi that doesn't have it.
2011 E90 M3 Space Gray/Fox Red/6MT/PP/CWP/EDC/PDC/Sirius/Rear Sunshade
2005 330i ZHP (sold)
2001 X5 3.0 PP/auto (sold)
2000 528i Sport/PP/5MT (sold)
1998 528iA Premium (sold)
1997 740i (sold)
1993 318is (sold)