We're probably a week to ten days or less from Manny Parra's return to the major leagues, and I think it'll be interesting to see what happens when he returns. I'm not sure who Parra will replace on the roster and, perhaps more importantly, I'm not sure what his role with this team can or should be.
First of all, I think most of us agree that Parra has run out of chances as a starting pitcher. Even if that weren't the case, he's unlikely to get a shot in the rotation at this point: He hasn't thrown more than 35 pitches all spring, so by the time he was stretched out and ready to contribute Zack Greinke would be back with the team and there likely wouldn't be another spot available for him.
Second, because he's left handed it's somewhat natural to assume Parra could be used to get tough lefties out. Unfortunately, his numbers suggest he wouldn't be very good in that role: He allowed opposing southpaws to hit .326/.400/.583 against him last season, and .277/.357/.446 for his career. Going by career OPS against, Parra isn't significantly better against lefties than most of the righties in the current Brewer bullpen:
* - There's probably a sample size issue with Kintzler, since he's only faced 14 lefties as a major leaguer.
** - Loe was much better against lefties in 2010, posting a .274/.311/.429 line for an OPS against of .740.
Finally, I've heard it suggested that Parra could work in long relief. Unfortunately, I think his tendency for meltdown innings would make him a liability in that role. A long reliever needs to be able to limit damage better than Parra does: A good one can be counted upon to eat 2-3 innings when a starter leaves early. They may give up a run or two here and there, but their primary purpose is to prevent their manager from having to use the entire bullpen to finish a game.
Parra's tendency to allow disaster-type innings makes him a relatively poor fit for that role. If he's called upon in the fourth inning, for example, and can't get outs, then the Brewers are going to have to burn through the rest of their bullpen just to mop up a likely blowout loss.
In the end, Parra's best role is probably short outings in the middle of games or late in non-save situations, a role you'd likely give to the fifth or sixth guy out of a seven man bullpen. And if that's the case, then the Brewers probably aren't going to benefit a whole lot from having him back.