Pros
Due to the company's small size, I was able to form a relationship with everyone there. Furthermore, I was given the opportunity to work on a variety of projects across multiple teams. I was never pigeonholed into one function or project, I was always given the option to work on projects that interested me. Overall, I was able to learn a lot because of this flexibility and I came out of the internship with not just concrete experience, but great mentors as well.
Cons
Due to the nature of startups, you have to be a self-starter with heavy ownership over your projects and the quality of your work. Oftentimes there won't be a pre-existing process or standard, therefore, it's up to you to figure out the best way to carry out and deliver a task.