Hernandez, who turns 34 in August, had struggled throughout most of his major league career, most of which was spent in the Cleveland Indians. He holds a career ERA of 4.59 and a K/BB ratio of just 1.64, but has found some success at varying points of his career. With the Phillies this year, he is 6-8 with a 3.87 ERA, though his K/BB has dipped to 1.36. He's managed to keep the ball in the park more (10% HR/FB), which was a serious problem for him in 2013 (20.9%) and in his brief 14.1 innings in 2012 (23.5%).
The Dodgers will likely keep Hernandez in the bullpen, with the possibility of moving him into the rotation if necessary. Though their rotation is fairly well set, it never hurts to have more options at your disposal. If there's anything that has defined the Dodgers season, it is keeping their options open, specifically with starting pitchers. They started the season with seven options for their rotation, and have been fortunate to rely almost exclusively on their big five of Clayton Kershaw, Zack Greinke, Hyun-Jin Ryu, Josh Beckett, and Dan Haren.
The Phillies, meanwhile, managed to move a starting pitcher, though it was likely not one that most people had considered being moved off of their roster this month. Cliff Lee, Cole Hamels, and A.J. Burnett are still in place, none of which are likely to be moved during the waiver trading period.