Pros
You get thrown right into project and start learning!
Cons
Because you get thrown in, there's no time to learn and be aware of all the qualifications you should be getting along the way. There's no structure. Also your ability to stick here is being lucky and learning a lot from your first projects that help you move onto other projects. Around my time I joined with 5 other level 1 engineers and we were all put into different projects based on randomness. At the end of one year the person who gained the most knowledge and experience from their own project was able to keep their job when people were getting let go. It's all luck and having connections within the company to stay afloat. The real test is your ability to find work once your work ends.