I think this is one of the most significant statistics of the game (in fact, of all six games).
Even if a team has somehow managed to cover our offense in the first three quarters, they won't have anything left for the fourth quarter. The Patriots' defense, on the other hand, should be reasonably well-rested.
This is why the Patriots can run off those 6-8 minute drives in the fourth quarter, preventing the other offense from getting onto the field. Yesterday, it came at about the 10 minute mark, when the Patriots got the ball. It was clear at that point that Dallas was finished.
I wonder what the records are for time of possession. I think it's almost as clear a sign of dominance as outscoring your opponent by 20 points a game.