Pros
Interesting work with an incredible amount of responsibility. Being able to be a part of a rapidly growing company that does not have all of its processes in place gives employees the opportunity to shape the direction of the organization. For entry-level employees, this is a great time to join a firm that's making good strides at solving some pressing strategic and operational challenges. The lack of formal structure gives you tremendous opportunity to build credibility in a rapidly growing firm through your in-house experience with proprietary product and processes that lead to rewarding career progression (promotion from entry-level Analyst to Manager (a role where new hires join with 5+ years of experience) as early as 2.5 years at consistent high-level of performance). The people in the company make the work so much more enjoyable. This is a very collegial workforce and most people are extremely intelligent, driven, yet willing to help. I've heard numerous people say "if it wasn't for the people, I would not have enjoyed working here as much".
Cons
One of the most worked (and stressed out) workforce. Hours are extremely long (especially for companies in the Bay Area), and also inconsistent across teams and teammates. There is also a severe lack of structural support given to teams. Employees get visibility about the different initiatives / strategies floating around the space, but most of these are high-level ideas. Teams are expected to take on a lot more than they can handle, and there is a lack of senior management recognition for that. Coupled with the lack of clarity on the structures that they are trying to put in place, overloading the workforce has led to one that cares a lot but feels non-empowered due to the lack of support.