Edit: Alex Wood will only be going to the bullpen for a week. He will start next Saturday's game, apparently.
A decision had to be made and this seems like the easiest one. The Braves want to limit Alex Wood's innings and the easiest way to do so is to have him pitch out of the bullpen for a portion of the season as Kris Medlen did a few years back.
With Gavin Floyd looking good in his first start and Aaron Harang proving serviceable through the first month of the season, the Braves now have six quality starters and one had to be moved out of the rotation. Fredi Gonzalez is understandably against a six man rotation as it keeps guys on rest for too long, so rather than ditch Harang altogether or use him as a long reliever they are opting to use Wood as the team's second lefty.
Wood was very impressive last year out of the bullpen. My only concern with this is that there is still unclear evidence on whether or not moving pitchers between starting and relief roles has any long term effects on their arms. Hopefully Wood stays healthy and provides value in the bullpen until he is brought back into the rotation when needed.