Courtesy of some basic projections, we know that Jeff Suppan is projected for a 5.43 ERA by CHONE this season. Manny Parra projects at 4.90, and Chris Narveson at 4.18 (though as a reliever, which carries a substantial benefit, he's closer to 4.7 or 4.8 as a starter). For clarity, I will just use Parra.
Parra .544 runs allowed per inning
Suppan: .603 runs allowed per inning
For every nine innings, that's an expected difference of a half a run (easy way to check this is to look at the ERA). Is that a lot? It doesn't seem like it. But it is.
If you believe the projections are accurate indicators of how these two pitchers will perform this year, giving Suppan about 150 innings instead of Parra would be a difference of about 9 runs, or about 1 total win on the field. That might not sound like a whole lot, but that win is a big amount, and generally teams pay about $5 million on the free agent market to upgrade their team by one win.
So if there's a point to this short jumble, it is that though it sucks to see Suppan scheduled to pitch tomorrow, a few starts will not make or break the team. The danger is continuing to run him out there. I don't know where the cutoff is. The flip side is that there is little doubt that every start Suppan makes is costing the team runs, and wins.
So hopefully management comes to their senses and realizes that Suppan has no real value in the starting rotation, or on the team, except as an injury fill-in. However, I'm going to avoid getting too worked up about Suppan being the starter (for a while, at least). Here's to him proving everyone wrong and coming out striking people out and avoiding walks with great command and control tomorrow.