Someone will need to dfa'd each time someone is added like Clevinger, Drury, Meidroth, Montgomery, Teel, Quero along with anytime a reliever goes down, unless you want to start throwing starting pitching prospects in the bullpen due to injury.
The 14 extra spots on the 40 man have to cover both guys you are protecting and guys you need as AAAA substitutes. It's not a lot of spots when you consider the number of pitchers we're likely to go through. It would be better to use 40 man on someone like Maton who could both cover in event of injury and potentially have use beyond this year