Well, in my case at 11:50pm last night.. local knowldge.  While coming home from an unexpededly long road trip, I came up to a part of I-80 that was (had been since 5pm) closed because of an accident.  Most the drivers, not being locals just pulled up to a stop and went to sleep while waiting for hours for the road to open, because they did not know how to get around it.  Luckily for me, I spoted an exit that I knew exacly where the road would take me.. and that was to a second road that would take me home.

The nav I had with me, could not find any routes around the closed road, so that was a 140$ paperweight at that moment.  But with knowing the roads, I only had to add 30 minutes to the drive instead of hours.  Granted, if I was in an area I did not know.. I probably would be one of those people sitting along side the road waiting the night out.