Betances had pitched 105.1 innings at Double-A before the promotion. He had a 3.42 ERA, but has struggled lately. From the end of June to the beginning of August he had a 6.32 ERA over eight starts. Only over his last two starts has he posted a 2.25 ERA that got him promoted.
Betances has an innings limit of 150 this season. If he pitches all of September he should be right at about 135 or so. That would give the Yankees room to play around if they wanted to call him up for a relief stint in September or even an emergency start. He is already on the 40-man roster so a move would not be necessary.