When I was recently asked why someone would need a coach I responded by saying, "nobody needs a coach". They looked surprised and confused and I added that, "I likely wouldn't have a client who felt they needed a coach."
People who 'need' coaches are usually trying to fix something that has gone wrong either in their lives or businesses. Certainly a coach can help fix those things, but usually someone who 'needs' a coach is someone who has let the problem linger for so long that it is affecting them negatively to such an extent that they can no longer ignore it and need help fixing the problem. In that case they most likely would benefit from hiring a consultant who can look at what has gone wrong and suggest ways to fix it, especially if it relates to their business.
The people who benefit most from coaching are not the people who 'need' a coach, but rather the people who 'want' a coach. People who want a coach are usually people who are high performers who are goal oriented and want to continue to grow and expand and they understand the value of coaching as a means to help get them there.
Coaches do many things as part of their craft, but in particular they are an objective pair of eyes who help the person they are coaching see or understand things they are otherwise unable to. Coaches use various tools and methods to help them gain insights and those "aha" moments that open up the road to where their clients are trying to go. It's those moments of clarity and understanding they gain that people who hire coaches value so much because those are the moments of transformation which can be truly life-changing.
While I firmly believe everyone should have a coach to help them become great in their lives, (yes, I've had coaches and will continue to have them) coaching isn't a necessity, nor is it a luxury, at least not to the people who are unwilling to settle and see the value of it to help them achieve greatness and the life they want.