Pros
The mission(s) can be extraordinary. LM is very flexible and people focused. You get out what you put in--if you want to excel and grow, you always have the room to do that. There are so many opportunities and different growth paths. Truly something for everyone.
Cons
YMMV on flexibility as it will depend heavily on your direct line leadership and specific program culture. However, general LM policies give a lot of great options for employees. Culture around the company can vary significantly from program to program. This includes everything from growth opportunities to recognition and work life balance to team interactions. Funding is very rigid and implementation of new innovations / technologies is typically slow (similar to healthcare, often there are many regulations to keep in compliance due to risk of life and risk of security breaches). If you aren't driving your growth, it isn't likely to happen in most areas. There is no common set up path for training and growth. You have to be proactive here; when you are, there are numerous resources and people that are more than happy to help you once you ask.