Purpose of auto-frosting windows?

We recently ran a story in the AASHE Bulletin about the University of Akron Wayne College's (OH) new Student Building.  The article from which we drew the story listed the structure's energy-saving features, one of which was "glass that spontaneously clouds or 'frosts' over when rooms are unoccupied."  I'm wondering about the purpose of the auto-frosting glass and how it compares to double- or triple-glazed windows, which are energy efficient all the time, rather than only when people aren't in the room.  Additionally, what's the benefit of auto-frosting glass over shades that automatically roll down when the room is unoccupied?