You seem to be thinking of "hunk" and not what Facebook calls "diff" -- what Facebook means by "diff" is closer to what many people call "commit" or even "branc

You seem to be thinking of "hunk" and not what Facebook calls "diff" -- what Facebook means by "diff" is closer to what many people call "commit" or even "branch", i.e. a set of interrelated changes that are sort of atomic. Reviewing individual hunks would be crazy and even Facebook knows that.