Pros
If you are interested in trying new positions but your knowledge in that specific area might not be robust enough and you would like to grow in that area, you can join projects that are in sustainment stage (of course, you have to be qualified for this position at a certain level to pass the internal project interview). You will be still expected to have high performance with established process and knowledge base, and also be expected to build enhancements to the current processes and deliverables. When you are specialized in certain area, you would like to join project in initiation phase to show case your skill. Therefore, this is a good place to launch/switch career in certain level.
Cons
Your success sometime depends on who you are following with. As the same as many places, you can encounter bad managers and great managers – especially, no all managers would be interested in representing your best interest.