Alas, the days when teams had one relief pitcher who pitched multiple innings are gone. Specializing relief pitchers is part of the game now, as we rarely see a reliever go more than one inning unless special circumstances apply (rain delay, blowout, etc.).
The whole point of specializing relief pitchers is to make them more efficient.
A lefty specialist can focus only on left-handed batters, and he usually comes in when another left-hander is up.
A set-up man pitches the eighth inning, bridging his job to the closer's. Nowadays, the closer comes in only in the ninth, and only in save opportunities.
The only pitcher that pitches more than one inning with regularity is the mop-up man. And since the mop-up man comes in during blowouts or after rain delays, he hardly pitches.
Don't forget to throw in a designated side-armer, knuckle-baller, or some other funky pitcher, as they are prevalent in a few MLB bullpens.
Where's the efficiency in all of that? At least three pitchers to play one game? Where have the days of Nolan Ryan, who once threw 259 pitches in a single game, gone?
Let's face it—pitchers are being babied. From Little League on to the majors, pitchers are not allowed to throw a lot of pitches. It's the general notion that if a pitcher who plays a nine inning game throws over 100 pitches, he's pretty much done. We will never see a pitcher throw over 150 pitches in a game again.
Now, we can see why starting pitchers are held back, as they throw more innings than relievers.
So why are relief pitchers held back?
The average relief pitcher today pitches about 1.2 innings. In the 1960s, relief pitchers averaged 2.3 innings per game. A 1960s relief pitcher pitched double the amount of innings than a reliever today pitches.
The huge difference is due largely to specialization. In the 1960s, there were no lefty specialists. There weren't any designated side-armers. MLB teams didn't have closer by committees.
Specialization has basically killed the number of innings a relief pitcher pitches.
Since there are more positions in the bullpen, roster spots go up.
More lackadaisical pitchers are allowed into the league.
Runs go up. Fans want runs. Owners want fans' money. Specialization will not die.
But would a lack of specialization lead to more wins for ball-clubs? Maybe.
Joe Nathan, the Minnesota Twins' star closer, was injured in spring training this year with a UCL tear in his throwing arm. Twins fans wondered what the Minnesota organization would do. Twins manager Ron Gardenhire decided to give 6'11" behemoth Jon Rauch most of the save opportunities this year. Rauch has done fine, converting 10 of 11 saves.
Was that the most efficient move for the Twins? Maybe not, but it has worked out well, as the Twins are in first place of the AL Central division with a record of 23-14.
Another possibility for the Twins' Nathan catastrophe was to have a platoon of Rauch, Matt Guerrier, Jose Mijares, and Pat Neshek for outs after the starter was done.
That would take specialization to a level unheard of before. So with Rauch becoming the closer, and specialization being on a looser leash for a little while, the Twins have become one of the top teams in the AL.
As you can see, specialization of relievers is not always necessary, but it will continue.