Pros
Defense contractors are focused on simply filling positions and keeping these positions filled. If you're a new or inexperienced software developer, then it's a smart strategy to gain the expertise you'll need when applying to the private sector. We call the private sector the "real world" as corporations are measuring product and not filled positions.
Cons
Management has no idea what products or services their employees provide. As long as the Government client is not complaining then all is well. One SAIC manager told a co-worker to "shut up and count your money" after she complained that the government client berated her. My advice, get in, acquire some skills, and get out. The only exception will be if they place you with a fair and professional government customer, because essentially, the government is your true management team.