For some reason, people think you should kick the xp when you score a TD to put you down 9 late in the game. Today was the perfect demonstration of why this is wrong.
Down 15, you either need two scores or three scores, depending on whether you convert a 2-pointer or not.
But you don't know how many scores you need until you attempt the 2-pointer. That's why you do it after the first TD.
If the Cowboys had kicked the XP after the first TD, they would have been down 8 and they wouldn't know how many more scores they needed. They likely would have been more methodical on the second TD drive, playing to tie (and not leave the Falcons enough time to win it). Then, if they failed the 2-point conversion, the game is over.
This way, they KNEW they needed two more scores, and they were much more aggressive on the second TD drive, leaving themselves enough time for the third score.
When down 15 late, ALWAYS go for 2 after the FIRST score. Information matters. And there's no benefit--none--to waiting.