I agree that there is a 'script'. I think much of that has to do with relievers liking having a set role. Also, much of it has to do with managing for the season and burning out any of the arms.
I strongly agree with the idea that a closer should be used in earlier innings if the game calls for it. Wednesday's game was a perfect example. The true save situation occurred in the 8th inning.
I have no problem with Barnes starting that inning. But once he walked the first 2 batters, and especially with the 4, 5, and 6 hitters coming up, it's time to bring Kimbrel in. Let Kimbrel get the 3 outs, then worry about the 9th inning when you get there. If Kimbrel can't go a 2nd inning, then bring in somebody else.
There is no sense in keeping Kimbrel on the bench for a save situation that may never come.