The Pirates have won 12 games in September. Five of them have been started by Gerrit Cole. The Pirates have lost 11 games in September. Zero of them have been started by Gerrit Cole. Here are Gerrit Cole's numbers in those five starts:
32 IP, 24 H, 39 K, 10 BB, 6 R, 6 ER, 1.69 ERA. Opponents are hitting .212/.276/.248 against him with a .324 BABIP, which means that we don't have to deal with any pesky Jeff Locke-esque questions about whether he's getting an inordinate amount of help from the defense. He has not allowed a home run and he's getting as many ground balls as fly balls.
Now, let me ask a hypothetical question. Let's say that on Sunday, when Cole is presumably scheduled to start next, the Pirates have nothing to play for. Let's say that the Pirates have home field in the wild card game wrapped up and that the Cardinals have clinched the division. Do you consider holding Cole back for the wild card game? I suppose if the game is at PNC Park, the answer is no. Francisco Liriano is more or less poison to lefties (they have a .303 OPS against him, which is even better than when Jonah Keri wrote about him having one of the best seasons in history against left-handed hitters for a starter) and he's been almost as good at PNC Park (Liriano has a 1.47 ERA at home and a .474 OPS against with 72 strikeouts and 26 walks, allowing only two homers in 73 2/3 innings) which is a great place for left-handed pitchers.
What if the opposite is true, though? What if the Reds beat the Pirates on Friday and Saturday and have home field for the wild card game wrapped up (if the Pirates and Reds end up tied, the Reds will host the game because in order for a tie to happen, the Reds will have to beat the Pirates twice over the weekend and that will give them a winning record against the Pirates this year)? Liriano has been good but not dominant on the road. Do you consider starting Cole holding Cole back on Sunday for Tuesday then? This is probably a thought exercise in futility, because I think Clint Hurdle will almost certainly go with the veteran Liriano either way. Since he'll be facing a lineup with Shin-Soo Choo, Joey Votto, and Jay Bruce, I think that that's probably the right decision no matter if the Pirates are at home or on the road for the game. Neutralizing those three hitters would be a huge advantage for the Pirates, and Liriano has a much better chance of doing that than Cole does. Still, it's a testament to Cole and his work this month that it even seems like this conversation needs to be had.
In the case that Sunday's game is meaningless, the Pirates will have two options. One would be to use Cole for a short start (even if it's only three or four innings) to keep him on schedule for Game 1 or 2 of the NLDS, since he hasn't looked right when he's pitched on extra rest this year holding him from last night's start until Game 2 (his most likely slot in the division series) will be nine days of rest. The other option is to hold him back, so that he can be used in the wild card game either as a long reliever (heaven forbid) or as a seventh or eighth inning guy now that the bullpen kind of sucks. I think you can make a strong argument for either approach (argument one: you gotta win the elimination games in front of you at all costs / argument two: the playoffs are a long chess match, and you don't know how Cole would respond to coming out of the bullpen anyway), and I suppose we don't really have to think about it until Sunday. Given the way this season has played out, it seems likely that the Pirates will need him to start then anyway and this whole conversation is moot.