Pros
I came from big corporate and found working at a much smaller company to be truly refreshing. You can put forward ideas and expect to be heard. You are given the creative freedom to think about how to solve problems and empowered by the organization to solve them. If you have talent, drive, and are a self-learner you will thrive here. But you will be put in many situations where you are the only one solving a given task and you may not have many people to lean on in finding a solution. So it can be a sink or swim situation if you are not confident in your abilities to do that. But if you are able to do well in such situations you will be recognized and rewarded for it. For me, it's been a dream come true.
Cons
Sink or swim. Can expect to be put in stressful situations where you need to complete a task by a certain time with no exceptions due to various constraints in the organization. And you have to figure it out for yourself from the ground up most of the time. If you are not able to this will be noticed immediately.