Pros
The responsibility afforded to young engineers at SpaceX is unmatched in the Aerospace industry. The magnitude and complexity of the projects force engineers to become self-reliant, efficient and often cross-disciplinary. SpaceX is incredibly nimble and is always willing to adopt new processes and tools. You will absolutely leave SpaceX as a better engineer…
Cons
…the downside: you will absolutely leave SpaceX. The work/life balance is atrocious and the compensation is frustratingly low considering that employees generally work 50-100% more than their peers at other companies (70 hr weeks are commonplace). You will not have time for hobbies, you will not have time to maintain relationships and you may not even have time to remain physically healthy.