It changes everything, just look at field position alone. Pittsburgh took the ball over on downs at their own 3, went 31 yards and punted. If Detroit kicks the field goal, Pittsburgh gets the ball around the 35. If they go 31 yards there they kick a field goal and negate Detroit's immediately. Not to mention they likely run different plays on their own 3 vs their own 35. Every single play call is made situationally, kicking a field goal vs going for it on 4th changes the situation of every single play after it and thus every single play call is different.