The loogy (left hand pitcher brought in to get only one out) has become more essential to the bullpen than ever before. In fact, name one team that does not use one. While there are some right handed pitchers who specifically come in to get right handed hitters out, bringing in a righty to face a righty depends on the team's manager. Some managers do it a lot more than others.
In regards to a LOOGY, many credit Tony LaRussa for its usage. Some vilify him for it, while others praise him. I am sure if we did enough research, we can go back further, but LaRussa started that philosophy with the White Sox in the early to mid 1980s. Guys like Jerry Don Gleaton, Juan Agosto and Kevin Hickey thrived in that role at different times. He also had an older Sparky Lyle and at times, used Jerry Koosman to get one lefty hitter out. Later on, with the Athletics, LaRussa used Rick Honeycutt to perfection, but he also had guys like Greg Caderet and Joe Klink.
Currently in the game, we all have our favorites, whether it is the Yankees Boone Logan, Sean Burnett of the Angels, Javier Lopez or Jeremy Affeldt of the Giants, Antonio Bastardo of the Phillies or Troy Patton of the Orioles (enter additional name here...). One thing they all have in common is the fact that they either struggled early on in their career or made the move to LOOGY later on. In other words, none of these pitchers came directly from their progression in AAA to the major leagues to be a left handed specialist. You find that more pitchers are being brought up that way, but many have a hard time making the adjustment to the big leagues.
The Mets have two left hand pitchers who are taking turns shuttling between the Mets and AAA Las Vegas. Josh Edgin was a late inning reliever, a closer, coming up through the Mets system. He was pitching against lefty and rightys in A and AA and it wasn't until spring training of 2012 when the Mets started using him as a LOOGY. Robert Carson was a starting pitcher two years ago, and not only has his role changed as a reliever, but not he is automatically expected to come into games and get one left hand hitter out. No wonder he has struggled. But, if you throw left handed, you should automatically be a specialist, right? I disagree.
Some of the best left handed relievers are guys like Jim Kaat, Jesse Orosco, Mike Stanton, Eddie Guardaro, Arthur Rhodes, Darren Oliver, Pedro Feliciano. Though each of their experiences are different, one thing they all have in common is the fact that they were, and in Oliver and maybe Feliciano's case, are veteran pitchers and were when they took on that role. Prior to that, of course, Kaat was a very good starting pitcher and Stanton (with the Braves) was an 8th-9th inning guy and Guardaro and Orosco were closers. The others bounced around until they figured out the art. To me, that is the pitcher I would look for to take on that role. Not a guy just up from the minor leagues.
The premium for left handed specialist has kept teams for using them as closers. In fact, only Cincinnati's Aroldis Chapman, Kansas City's Tim Collins, Colorado's Rex Brothers and Minnesota's Glen Perkins currently throw from the left side and close. (Pardon me if I missed somebody). Even Chapman a couple years ago had to battle to get that job as the Reds wanted him to kind of take on the role of a LOOGY. Though they are both hurt now, the Braves had the luxury of having two dominant left handers in Jonny Venters and Eric O'Flaherty. This gave them the opportunity to use one for a batter or two (mostly O'Flaherty) and the other for the 8th inning. Prior to their injuries, they were the one exception to what I have said.
The fact that a pitcher pitches left handed does not make them a good left handed reliever, especially when the responsibility is to only get left hand hitters out. The best left handed hitters in the game know the makeup of a LOOGY and in many cases, can get a hit 1 of every 4 or 5 times against one. Experience has a lot to do with pitchers who have thrived in that role. Greg Swindell made that transition at age 32, and added 6 years to his big league career. It had something to do with the fact that he knew how to pitch to leftys, something he developed with experience. Honeycutt at age 34, took on the role and pitched until he was 43. Both were starters but had the understanding of what it takes to master that role. How can you expect a 22-23 year old pitcher to come up and only get one batter out every game? It takes mental toughness that many rookies and minor leaguers simply do not have at that age. So please stop with the thought that anybody that throws left handed can simply take on that role.