Pros
An excellent place to work, whether you're just starting out or an expert in the field. The startup setting often poses fairly challenging tasks that need to be solved from scratch and in uncharted areas, but the open working environment offers complete freedom in selecting paths to their solutions, encourages new ideas and visions. Cross-functional teams following agile development methods include individuals from various backgrounds, and provide guidance, advice, and perspectives on tasks from different angles. The internal culture encourages personal development and provides ample opportunity for sharing experiences and knowledge among employees.
Cons
The autonomy in one's own tasks may not suit all people, often there are no conventional approaches to tasks and one has to invent things on the fly. This environment requires the ability to adapt quickly to changing conditions and not be afraid to fail and start over.