Pros
The mentoring progam allows you to learn more about the practices, clients and office politics without putting yourself in a compromising position. My supervisor is very aware of my workload and when things are piled, we communicate and adjust things so I'm not completely stressed out. The accounts I work on are far better than my peers at other agencies.
Cons
The hierarchy and cliques can make it difficult for a junior staff member to speak out and work collaboratively with others. Also, the immediacy of certain client needs are usually not that immediate. Senior level employees tend to promise the client deliverables before consulting with the junior level staff who actually produce those deliverables and many times this puts pressure on the junior staff to work on tasks that are impossible to accomplish.