Pros
Incredible people. You will work with the best of the best. Smarter and more accomplished people than Google or Facebook, many with significant Open Source contributions or independent Data Science accolades, scientific awards, books published, patents, research positions at elite institutions, you name it. Very challenging problems --- most of the technical challenges here are deep and require solutions that bump against the frontier boundaries of the tools used, so you gain a low-level knowledge and must come up with creative solutions. Also there are ample opportunities to be recognized for your work if you are willing to work and have the courage to ask to work on hard things. People are very friendly and willing to help and offer mentorship.
Cons
Related to the Pros. Problems can be difficult and can be time consuming, but if you pass the high standard for hiring then you can probably handle the challenges. You will have to always be learning here since the software stack is complex.