During the season, it's often said that a team "needs" a strong outing from its starting pitcher to save the bullpen after a game in which the relievers were worked heavily. Those games don't happen real often, but it's also been suggested that a long outing from a starting pitcher allows the bullpen to rest up, generally, which is a good thing.
Is it, though? Beyond the Box Score's Bryan Cole tried to find out:
To this point, it has been difficult to quantify the exact contribution of this effect on a team's long-term success ... the authors of The Book found that relievers "can handle a much heavier workload than current managers are imposing" without diminishing their performance. This suggests that bullpens may not need as much saving as is usually assumed.
From this analysis, we conclude that the efficacy of "saving the bullpen" is overstated, and that there is little if any carryover effect on the bullpen from a longer outing by a starter.
I skipped over all the actual analysis. It's semi-complicated, but the conclusion is clear.
Bryan allows that his study could have been more sophisticated, but his results are perfectly consistent with the idea that bullpens rarely need to be saved, and that relievers can pitch more innings than they typically pitch. We did conclude some years ago, rightly or wrongly, that 100-plus innings for a relief pitcher wasn't a good idea.
Last season, nobody pitched 100 innings. Two relievers were in the 90s -- let's hear it for Anthony Swarzak and Josh Collmenter! -- and only five in the 80, while 26 were in the 70s. As far as I know, there's never been a study showing that 75 innings is safer than 85. I wish I could suggest that asking relievers to throw more innings would mean fewer relievers (and more hitters!). But I don't think it would. I think it would just mean more pitching changes.
Bryan was testing the idea that a durable starting pitcher has some extra value, beyond just preventing runs in the innings he actually pitches. This test suggests that he does not.