The Atlanta Braves and closer Craig Kimbrel agreed Sunday morning to a four-year contract extension worth $42 million with a $13 million club option for a fifth year. The deal is the second-richest contract extension for a reliever to Joe Nathan's four-year, $48 million deal with the Twins in 2008, and it is the largest ever for a reliever yet to accrue four years of service time by $27 million.

That is to say, the Braves just paid Craig Kimbrel like the once-in-a-generation talent he is. As a result, the three-time All-Star, a 25-year-old who has earned Cy Young and even MVP votes in each of his three seasons, is now in line to be the Braves' closer through age 30.

Kimbrel set a career high with 50 saves in another dominant season in 2013. He recorded at least one strikeout in 56 of his 68 appearances and struck out 13.2 batters per nine innings, which sounds impressive until you realize it's a career low. Kimbrel's 14.9 K/9 since becoming closer in 2011 ranks best in the league among all pitchers with at least 20 innings pitched. In a league where so many teams feature home run hitters throughout the lineup, the only guaranteed way to hold a one-run lead is to not let the hitters make contact in the first place, and few are better at missing bats than Kimbrel.

But whenever a reliever gets such a large payday, questions arise about the wisdom of spending so much on a player who spends such little time on the field. As important as the ninth inning is, Kimbrel's 67 innings only account for roughly six percent of the team's yearly total. Kimbrel, particularly towards the end of his contract, will likely be earning 10 percent or more of the Braves' total payroll. The ninth is important -- and it is just the ninth, as Kimbrel didn't have a single appearance over one inning last season -- but is it that important?

It's a tough question that doesn't have a clear answer. Some recent moves -- see Francisco Rodriguez's $37 million contract with the Mets or Jonathan Papelbon's $50 million pact with the Phillies -- have shown a great closer alone will struggle to lift an otherwise poor team. Other moves -- like the Red Sox's $4.25 million signing of Koji Uehara -- have shown great free agent closers don't have to be expensive. Some teams, like the Cardinals with Jason Motte and Trevor Rosenthal, have shown the best bullpens can be grown from the farm. In fact, the Braves have served as one of the finest examples of this bullpen-building strategy behind Kimbrel, Jonny Venters, Eric O'Flaherty, Luis Avilan and others racking up the outs at league minimum salary rates.

As such, it sounds like a relatively simple choice to take your chances on a cheap bullpen while focusing financial resources on building position player and starting pitching talent. But this ignores just how big a difference an elite bullpen can make. Consider the 2012 Orioles, a team that was actually slightly outscored over the first six innings (504-511) but managed to win 93 games in large part because Jim Johnson, Darren O'Day and Pedro Strop all posted sub-2.50 ERAs in the back end of Baltimore's bullpen. Or consider the 2010 Padres, a team that was tied with the eventual World Series champion Giants entering the final weekend largely due to the unhittable back-end duo of Heath Bell (1.93 ERA, 191 ERA+) and Mike Adams (1.76 ERA, 210 ERA+).

The 2013 Pirates (Jason Grilli and Mark Melancon), the 2012 Athletics (Grant Balfour and Ryan Cook), the 2008 Rays (Balfour and J.P. Howell) are just a few other examples of recent teams to ride great bullpens to unexpected success. According to FanGraphs, each of these five teams had bullpens contribute at least eight wins above average by Win Probability Added -- enough to make or break a playoff season in each case.

However, as this list of names should help prove, it isn't as easy as dropping multiple millions on the latest top free agent closer and calling it a day. It takes career years and teams who happen to play a disproportionate amount of close games for a bullpen to make the kind of impact that suggests relievers should earn megadeals like Kimbrel's. Too often, they spend too many important moments in the bullpen to be the kind of swing player to justify it.

But on the right team, such a player can be extremely valuable. According to Win Probability Added on FanGraphs, Jim Johnson's 68.2 innings for the 2012 Orioles contributed 5.35 wins above the average player, more than every single player in the league. It was more than top hitter Mike Trout (5.32), and well above top starting pitcher Justin Verlander (4.04).

It would be absurd to suggest Jim Johnson in his 68 innings contributed more to the Orioles than Mike Trout's daily contributions to the Angels, or Justin Verlander every five days for the Tigers. Trout and Verlander aren't deployed so selectively, and so Trout will inevitably hit a few home runs down by double digits, and Verlander will pitch into the eighth of a few 7-1 games. But Johnson was so consistent in make-or-break scenarios for the Orioles that his excellent performance was enough to move the needle even more.

This seems why the Braves are willing to make this kind of move. Kimbrel is so dominant, so unhittable that his 60-70 innings will be worth around $10 million on a yearly basis. But if there comes a year like Baltimore's 2012 or Tampa Bay's 2008 or Pittsburgh's 2013, and the difference between making the playoffs and finishing under .500 is a lockdown bullpen, the Braves can be confident they have the world's best handling the ninth inning, and such a performance will be worth much more than even the $13 million Kimbrel could earn in the contract's option year.

So much of crafting a bullpen is a gamble. Performances over 200 innings are hard enough to predict; performances over the 30-70 inning range relievers occupy defines a crapshoot. Injuries wreak havoc on bullpens just like they do starting rotations. And then you need the lead at game's end for it to all be worth anything. This is typically the folly of the team that tries to spend its way into a great bullpen: too many things can go wrong, and eventually, something will. With Mariano Rivera off in the sunset, Craig Kimbrel is as close to it gets as an automatic three outs. It's as close as the ninth inning has to inevitability any more, and that's why the Braves are willing to cough up $42 million for Kimbrel to pitch the ninth for Atlanta for the next four years.