>There's nothing wrong with "Sarah Brown Eyes" as a song, but it does nothing to advance the plot. It simply panders to the audience's desire to see Audra McDonald (or in LA, La Chanze) come back again. "Sarah" and "Back to Before" are I want/I am songs, respectively, that would work fine in Act I--except that Act I is so tightly constructed there's no room for them there.<
Regarding "Sarah Brown Eyes," it's in Act 2 for a very specific reason, other than bringing Audra McDonald back for one more song. By that point in the act, Coalhouse is fairly deep into his acts of vengeance and the plan to blow up the Morgan Library is about to be hatched. "Sarah Brown Eyes" is a quiet, bittersweet moment that reminds the audience of Coalhouse's humanity and all that he's lost. It has no reason to be in Act 1, where it would be completely superfluous. No, it's not a plot song, but were it to be cut, you might otherwise have a pretty relentless, less sympathetic Coalhouse.
Begin at the beginning and go on till you come to the end: then stop.