David Price did, Liriano did it, Johan Santana did it. Some teams believe that getting a pitcher experience against major league hitting through the bullpen is a good way to ease them into becoming a starting pitcher in the majors. Some have failed, some have succeeded. Only a few teams have adopted this philosophy. Right now the Mets are banking on it with Jenrry Mejia and I'm not sure about the Cubs, but it seems like Andrew Cashner is also going the same route.
Joba did well his first two years, but instead of sticking it out after his first full year as a starting pitcher last season, the Yankees decided to put him back in the bullpen.