Here's my take on the signing from back in March 2013:
"The Arizona Diamondbacks' bullpen issues in the past several years have been well-documented, and after giving up top prospect Matt Davidson for White Sox closer Addison Reed earlier in the off-season, they've also acquired several other arms, as well.
Most recently, they have added left-hander Oliver Perez on a two-year contract worth only $4.25 million – not a lot for a good reliever. After his career as a starter went south in ways no one could have predicted, Perez has reinvented himself as a relief pitcher in the past two years with the Mariners. His 2013 was very good, amassing 0.7 WAR as a reliever – a solid total.
Perez is not just a lefty specialist. He deals with right-handed batters fairly well, but he is definitely tougher on left-handed batters. It was a bit surprising that he signed so late in the off-season, but the Diamondbacks should have a good deal here. Left-handed relief is definitely a need for them, and Perez fits the bill well without breaking the bank. While Arizona's moves in recent years and even this off-season have been greatly questioned by many, this deal is a good one."
2014 & 2015 Breakdown:
As it turns out, the Diamondbacks were extremely awful in 2014. However, Oliver Perez was definitely not the reason for it, compiling 0.4 WAR (0.6 WAR according to FanGraphs), which is a great total for a reliever, with a 2.81 ERA (3.15 FIP) and a 11.5 K/9 vs a 3.28 BB/9. It was actually an improvement over his very good 2013 with the Seattle Mariners. The Diamondbacks did get a steal with Perez.
Not only that, but Perez was good for the Diamondbacks again in 2015 - 0.4 WAR. They ended up trading him to the Houston Astros for minor league pitcher Junior Ortiz in an August waiver wire deal. While Ortiz hasn't panned out as of the end of the 2016 season, it would be a good deal. Perez blew up for the Astros, costing them -0.7 WAR in only 12 innings pitched in 22 games! Perez went to the Nationals in 2016 and was roughly replacement level.
The D-Backs signing of Oliver Perez is the perfect case of getting the most value out of a bargain, then knowing when to let him go. Too bad they haven't been this successful on most of their other moves.