The team acquires depth and makes a DL move that had to happen eventually.
With Cameron Maybin's injury the team was still not exactly hurting for depth, but could always use a little extra. Alex Castellanos has experience as a corner outfielder as well as at 2B and 3B. He started out in the Cardinals organization as a 3B, but moved to the OF in 2010. After being traded to the Dodgers in exchange for Rafael Furcal in 2011 he eventually began to split time at many positions including a handful of games in CF. In the minors he has had some very good seasons at the plate as well as some so-so ones. He got cups of coffee with the Dodgers in 2012 and 2013, but the bat did not translate in those short stints. Last October he was traded to the Red Sox, who tried to sneak him off their 40 man roster, but then was claimed by the Rangers who then tried to do the same before the Padres snagged him. At 27, there is still some hope though that if he got some regular time in the majors as a utility player that his bat could come around.
Before acquiring Castellanos, the battle for the final roster spot among position players seemed to be between Tommy Medica, Ryan Jackson, Reymond Fuentes and Rene Rivera (assuming Yasmani Grandal is ready for the Opener). Castellanos can add himself to the mix. I also think that with Castellanos now on the roster, anybody that had hope for Xavier Nady making the team (are there any of those?) can kiss that dream goodbye. Nady is not on the 40 man roster and does not have the positional flexibility that the others do.
As for the backend of this transaction, Cory Luebke moving to the 60 day DL, that was bound to happen eventually. He is not going to play this season and moving him to the 60 day DL opens up a roster spot for someone else. In this case it was Castellanos, which is as good a move as any. I had thought previously that they would save the roster spot in case they wanted to add a reliever like Leonel Campos or Kevin Quackenbush.