Pros
Lots of freedom to grow and develop if you're lucky to have a good manager. There are a few managers that will give you opportunities to learn and empower you to raise your status. The office can give generous bonuses during successful years. They also try (but usually fail) to create a positive and lax work environment. The happy hour on Fridays creates an appearance of camaraderie, but really it's surface deep. Most people have too much work to actually attend.
Cons
Many of the managers (senior associates) are TERRIBLE. These are folks who merely stuck around long enough to get a promotion, but really lack communication skills and management skills. Quite a few are temperamental and fail to give clear direction. The office's practice of promoting loyal employees or talented designers should be a good thing, but because there have been so many senior associates with poor management skills, the most talented staff end up leaving before reaching senior associate status. This creates a revolving door environment that the partners probably like to tell themselves filters out the lazy/poorly equipped staff but more realistically filters out the most ambitious and hungry designers leaving just the timid and ambivalent staff to remain. Also HR could offer more solutions to these issues but remains typically silent//powerless.