Pluspunten
If you prove yourself dependable to ownership, then you will gain autonomy. Yes, this studio is very busy and there are often late nights - but, this is a frequent issue in the industry, especially since workplaces became smaller during the recession. The fact that this studio is busy is a benefit - you will learn a lot. You will become an expert in multi-tasking and time management. Also, the clients are often large companies so you will have a chance to interact with important stakeholders, and the projects are usually high end (as in you often will have larger budgets than what you see at other studios - so more fun).
Minpunten
The environment is demanding, but I think this is sort of a pro as it prepares younger designers for the "real world." Salaries could be higher, especially since this office is in El Segundo and rents anywhere within a reasonable commute are too expensive for the average employee.