The quality of the voice is. It's very important that you work with a good coach. Often with singing teachers, they teach technique. But singing is so psychological and emotional.
People have a lot of emotion when it comes to that. Find a coach who understands what is happening to you psychologically so he can bring you back. However, your goals must be realistic and achievable. Voice lessons will improve the sound you already have, but they won't guarantee you a singing voice worthy of fame.
Everyone can learn to sing better, and a voice teacher can help you learn how to use your voice to the best of their ability. If the goal is to access your full potential as singers with an emphasis on an easy, natural sounding tone, you're in the right direction. And while singing lessons are the best way to improve your voice, the Internet has made learning to sing for free easier than ever. The work of a vocal coach is based on the assumption that a student is already capable of singing well and only needs training to achieve a goal.
And even someone like Barbara Streisand has dealt with a big stage fright in her life, so maybe that could have been something she could have worked on with a vocal coach. This can definitely require some preparation and is also where, sometimes, a vocal coach could come in handy. I think coming to a vocal coach is very important because, first, you can do the job, and second, trust. People come in different sizes and shapes, so the “best way to sing for anyone is the way that leads to the best (or most pleasant) result, without causing damage to the vocal cords (more on vocal health later).
While a vocal coach can also use the title of “voice teacher”, they may not have the same level of education. Some students looking for a vocal coach may be preparing for an audition or are studying a character for a performance.