Pros
The best, most intense and interesting learning experience ever. The moment you know what you do and start wearing your hat in a cosy way, something is bound to change and kick you out of that comfort zone into new challenge. Every day I come to a different work. Challenging, rewarding, crazy fast-paced, great for learning and development if you raise your hand and and are proactive about it. No one will offer you opportunity just because you sit at your desk and look fabulous. Not even because you are fabulous at what you do. You need to keep volunteering to take the extra work and help with another project and create your own chance to learn. No classrooms needed. Just tons of proactive attitude and willingness to try new things.
Cons
You have to perform outside of the standard scope of your duties to be promoted to the level you would have operated at for while beforehand. "Prove you can do it" approach