If your name is God then you don't need a mentor or a coach. For everyone else, let's explore the value of having one.
First some definitions. A "coach" operates with an organizational focus and is often assigned to you. Coaches have a vested interest in seeing you improve specific skills and interpersonal relationships that pertain to your job and how it impacts your company's bottom line. A coach's conversations with you tend to be more directive because the task of a coach is to help you achieve explicit workplace objectives and goals.
On the other hand, a "mentor" is someone whom you select to help you grow in various aspects of your life, with an agenda set by you. The purpose of a mentor is to help you where you want the help. In this role, a mentor acts more as a concerned questioner, facilitating your discovery of how you can improve upon the various issues you want to address.
Although the terms are often used interchangeably (which sometimes causes some misunderstandings), you can see there is a difference between coaches and mentors. One is selected by you to help you focus on your individual growth, the other is someone at work who is charged with helping you meet organizational goals. Unfortunately, many people today call themselves coaches when in fact they are serving in the role of mentor (and even I am guilty of that).
In reality, it probably doesn't matter which term you use, so long as you have a clear understanding of the purpose of the relationship. But, as I said, a lack of clarification can cause misunderstandings.
For example, a colleague and I were once asked to meet with the leadership team of a high-profile company that manufactures golfing equipment. They wanted some outside help to relieve tension on their leadership team. At the initial meeting, a senior vice president arrogantly sat back and challenged us with "So - what do you guys know about golf clubs?"
Without batting an eye, my colleague responded: "Nothing. And we don't want to know anything about golf clubs. We're experts in workplace relationships."
Even recently, someone came to me after opening her own business (for privacy's sake, let's say she sells widgets), and a relative of hers questioned her action, saying "what does he know about widgets?"
Within these examples, you can see the misunderstandings that arise. But either way, let's examine just a few of the benefits of having someone as a confidant, be it a mentor or a coach.
1. You'll gain clarity because you're often too close to a situation to see it clearly. Stated another way, it's pretty hard to see your nose, isn't it? It is literally too close to your eyes, and you just can't see it very well. Having another person sharing his or her insights about your situation gives you an outside perspective on how to improve. If you are motivated to make improvements, you'll place a lot of value on that person's perspective.
2. You'll have accountability. Without accountability we usually end up with a lot of blame or a lot of excuses as to why things don't get done. Sometimes both. Because it's difficult to be accountable to yourself (not impossible, but quite difficult), having someone to whom you're accountable helps you stay on track with those non-urgent but important actions which lead to personal and professional growth.
3. Coaching and mentoring is custom tailored to you. You can attend all the workshops and read all the books you want, but they will forever be delivered to a bell curve of people, not specifically to you. In coaching and mentoring relationships, everything is customized to meet your individual needs. You'll have to become vulnerable to some degree and acknowledge your human frailty, but a good mentor or coach is looking for ways you can capitalize on your strengths while compensating for your weaknesses. That just can't happen in a workshop the same way it can during a one-on-one.
It doesn't matter whether you decide that a coach or a mentor is better for you, but I recommend you get one. Even after 22 years performing the role myself, I follow my own advice. I have a "coach/mentor" to whom I remain accountable for my personal & professional development. For the record, I'm not fishing for more coaching clients. I just believe that unless you're God, everyone has room to grow.
As a final word, be sure that whoever you select as a mentor/coach is qualified for the job. This field does not require a license, so anyone can say they're a coach. Also make sure you don't get forced into any long-term contract, and be confident that whoever you work with maintains your best interests at heart. Investing in yourself always brings worthwhile returns.