The Pirates' recent flurry of roster moves (Jose Ascanio has been sent to the DL, Jeff Salazar has been designated for assignment, and Brian Bixler and Denny Bautista have been recalled from Indianapolis) demonstrate that the Bucs badly need relief help right now. There's no indication that Bautista is a legitimate answer; he has a track record of repeated failure in the major leagues, and nothing he's done this year suggests that this time up will be any different. He struck out more than a batter an inning at Indianapolis, true, but he also has walked 34 batters in 48 innings to go along with a 4.88 ERA. He'll also be 29 next week. Even as a placeholder on a floundering team, he's an uninspired choice.
So why not give Dan McCutchen a spot in the 'pen? McCutchen has had an interesting season as a starter for Indianapolis, posting a 3.40 ERA to go with 99 strikeouts in 129.7 innings. More importantly, he's improved to the point of being nearly unhittable over the course of the season--he posted ERAs of 3.74, 4.82 and 4.50 in April, May and June, respectively, but he had a 2.10 ERA in July and now has a 1.35 ERA in August. He has also struck out 36 batters in July and August while walking only four.
There isn't really a rotation spot available for McCutchen right now, but the bullpen is a different story. McCutchen will be 27 in September, so there's no good reason to hold him back if he can be better than one or more of the Pirates' current relievers. That is, his upside as a starter isn't so great to worry about using him as a reliever, and he's not so young that the Pirates should be concerned about service time issues. And it isn't as if the Bucs should be thrilled about their current bullpen.
McCutchen still has flaws--his strikeout rate is still a bit low, and he still allows tons of fly balls. (Of course, Bautista allows tons of flies too.) But the bullpen is, ideally, where flawed pitchers should go, because short outings can mask flaws. If an opportunity presents itself later, the Pirates could still move McCutchen back to the rotation, or use him as a spot starter, but why not give him a shot as a reliever now, while there's opportunity?