Best Friend -vs- Coach
At one point or another, we have all turned to friends for advice. We detail the situation, and look for their opinion. Generally, what they say makes total sense and supports us. Why would you decide to work with a coach when you have friends you can talk to for free?!
Short answer? Unbiased support.
Your friends and family are naturally inclined to offer their opinion on what they think you should do. Your decisions might even directly affect them and therefore, they will be invested in an outcome that is pleasing to them. Their advice and opinions are valuable and you should feel comfortable talking with them. However, their opinions are not unbiased and generally are not always objective.
Working with a coach, you'll find that their agenda is your agenda. They are invested in a collaborative relationship with you that is objective, supportive and free from judgement.