Suffice to say, the search in Atlanta for capable relievers that throw with their left hands continues. After a long tryout featuring a number of lefty arms, the Braves broke camp with just one lefty reliever: former Brave Eric O'Flaherty, who was acquired from the Pirates. O'Flaherty's second tenure with the Braves has been disastrous, featuring a 6.75 ERA / 8.51 FIP and seeing him allow 44% of batters faced to reach base. The Braves bolstered their lefty relief ranks with Hunter Cervenka, a minor league journeyman who's yet to allow a run as a member of the Braves organization. So far, Cervenka has struck out about 40% of the lefties he's faced, but he's always had control issues, and the Braves don't seem content to rest on his small sample size laurels.
To that end, they have made a move to sign Sean Burnett to a minor league deal after he opted out of his contract with the Dodgers. Burnett was a fixture in Pittsburgh and Washington bullpens from 2008-2012, where he exhibited the usual reliever volatility but also some very good seasons, including 2010 (2.14 ERA / 2.73 FIP) and 2012 (2.38 ERA / 2.79 FIP). He signed a free agent deal with the Angels prior to 2013 for two years and $8 million, but a left elbow impingement, followed by a torn UCL, derailed his career and he pitched only about 10 innings overall for the Angels over the next two seasons.
Even his 2016 has been an adventure already: he was in minor league camp with the Nationals, was released and signed on with the Dodgers despite drawing some interest from the Braves, and has now opted out of that contract to seek a spot on Atlanta's roster. Expectations shouldn't be very high, as Burnett has allowed six walks in fewer than eight innings of work for the Dodgers' AAA club, but he's been good before and may represent a better option than whatever the Braves can get from O'Flaherty at this point.
For his career, Burnett has kept lefties to a sub-.300 OBP (3.51 FIP). As with many lefty relievers, he's likely best utilized only where he has the platoon advantage, as righties have knocked him around (4.58 FIP). My own personal guess is that if he's called up, he'll be marginally better than replacement level, which would actually be pretty good in the types of bullpens Atlanta has been running out of late.