Working together is a partnership.
Together, we find the character. To me in my experience it is impossible to direct yourself and find everything you need to build a complete character. Together we will bring out aspects of a character and the larger ideas within the role.
For commercials we will breakdown down the text together, find what that one thing; that one overarching idea that emphasizes the product and puts you and what you are selling in the best possible light.
Having an acting coach is your accountability partner helping you to be at your best, for auditions, and work together to achieve your best performances no matter the circumstances.