David has not pitched for the Yanks since May 11th, and since then the Yankees are 18-11 (.620 winning percentage). So on the surface it looks like the team has been fine without D-Rob, but the stats tell a different story.
"You miss me because I can do this."
Now sure, in the previous 30 days,Yankee relievers have put up a 3.9 WAR, which is 4th in the American League (5th in MLB). But after that things go downhill. Their ERA was 3.84, which is 7th in the AL. The bullpen's FIP has been 3.49 , which is 9th in the younger league. Yankee Relievers WHIP...1.25, 12th in AL. And finally the reliever's batting average against over the past 30 days was .234, which is 10th in AL.
So I'm going to go out on a limb and say that getting back David Robertson, and his career ERA of 3.00, FIP of 2.82, WHIP of 1.33, and BAA of .216, is a really good thing. Okay, so his WHIP isn't that good, but we all know about Robertson's magic act, where he'll let runners get on but never allow them to cross the plate.
So the only question that remains is "who loses their roster spot?" River Avenue Blues has a good post (surprise!) that goes over the options for making room, so no reason for me to write 'em out for you. So I'll just tell you my response to this question...
"Hmm... not work but a few times a month, or the minors?"
Besides the fact that he hasn't done anything over the past 11 days (9 games), David's days as a starter are not over with. So why not send him back down to AAA, that way he can start games again regularly and the Yankees have an option for the rotation next season and the future? The bullpen doesn't need him, as Freddy Garcia is already in the bullpen, meaning the team right now has two long men. Back when the Yankee starters were throwing to a FIP of 4.91 (their May number, which was 11th in the AL) it made sense, since they needed a long man like every other day. But now that the starters are going much deeper into games, and throwing to a FIP of 3.96 (their number over the past 30 days, which is 3rd in the AL), it makes zero sense to keep a second long man on the roster.
Now some people may say at this point "then ship out Freddy Garcia". Well, like Mike at RAB pointed out in that post, you never know when things are going to go downhill again, and Freddy may be needed to make a start or two or three. Starting depth has a tendency to go away really quickly. And that doesn't get into the fact that the Yankees could end up paying Garcia to pitch someplace else, as a team that claims him off of waivers would only be on the hook for the remaining portion of a minimum salary. So let's try and get as much value out of Sweaty Freddy as we can.
"What do I want? LOL, as if anybody cares what I want."