A big selling point of DVDs and Blu-rays are exclusive commentaries from the directors and actors. They explain the reasoning behind certain scenes, or how some crazy special effects happened. Movie buffs understandably eat this chatter up.
Looper director Rian Johnson even made one that you can listen to in the theatre. But do you care enough to go see the movie a second time?
Arnold Schwarzenegger's epic Total Recall commentary is a given, but do you otherwise watch DVDs with the commentary on?