Since they moved back the XP, it actually makes more sense to go for 2 every time, going by league Average.
I think the math is something like If you went for it 300 times, you would get a +1 differential vs doing just XP.
Also, it affords the team real game time practice in goal-line situations.
However, situationaly, each team should analyze their kicker (Bills have a good one), the opposing defense, and their offense' red zone efficiency (Bills have a bad avg). So Buffalo shouldn't doing it that often. Additionally, they should stop kicking XP when the game gets out of hand.
It's similar to what happened in the NBA with 3point shooters.