Pros
You get to work with a variety of big name clients and get connected with a lot of people in the industry. They are willing to teach you how to be a better designer and give you opportunities outside of your unit in things you are passionate about (ie animation, film editing, article writing)
Cons
The timesheets are pretty rough. You have to track every waking moment to a client, so it basically insures that you are working a 7 hour day, not including internal meetings. They go through a lot of turnover so you will be working with a variety of project management standards, design requirements, deliverable expectations that aren't necessarily communicated to you. You'll be guessing a lot and putting in a lot of time just to figure out the next steps.