Vantaggi
You get experience fast, and usually you get to work with some very smart people. Your "PD Manager" has a lot of sway in your career development. It's a third party, and this is a very good setup. If you get a good one, this can make all the difference.
Svantaggi
Political culture, lack of mentorship. Management is by and large not very inspiring. In fact they are rather transparently self-serving. If you're not personally connected to management or being mentored by someone in the management group with pull, particularly your PD, you are unlikely to succeed or stay very long, or else your work life will suffer. In technology you can expect to get no technical development if you work "onshore". You are being prepped for management / B-School.