Granted, it's been a while.
Tyler Kepner (via The New York Times):
Once upon a time, the Pittsburgh Pirates made a habit of trading for left-handed starters for the pennant race. In 1990, they acquired Zane Smith from the Montreal Expos. Two years later, they snagged Danny Jackson from the Chicago Cubs. Both times, the Pirates made the playoffs.
They have not been back in the two decades since, of course, and they have not even had a winning record. Now they are 54-42 and aggressively aiming for a playoff berth.
Ah, but while it's one thing to acquire a starting pitcher, it's quite another to acquire a starting pitcher who actually makes a real difference.
In 1990, Zane Smith pitched brilliantly after the deal, going 6-2 with a 1.30 ERA down the stretch. He did not fare as well in October, getting tagged with losses in both of his League Championship Series outings. Worse, among the three players the Pirates sent to Montreal in the trade? Moises Alou.
In 1992, Danny Jackson went just 4-4 in 15 starts after joining the Pirates, with a 3.36 ERA. Jackson started one postseason game, and didn't survive the second inning. To get Jackson, the Bucs sent Steve Buechele to the Cubs; the third baseman did enjoy one solid season in Chicago, before declining rapidly.
Oh, I almost forgot the point of the things ... In 1990, the Pirates finished with a four-game lead over the second-place Mets, so you might argue that Zane Smith might have made a difference. Probably not. But maybe. In 1992, the Pirates finished with a huge lead, and would have won easily without Jackson.
So the results have been mixed at best. The Pirates gave up Moises Alou for Zane Smith, who didn't help much in 1990 but pitched exceptionally well in 1991. They gave up Steve Buechele for two-and-a-half months of Danny Jackson, who didn't help at all.
This deal has a good chance of working out better than either of those, because none of the players going to Houston are likely to be as good as Moises Alou. But it will be a few years before we know for sure.