A coach is an external set of eyes and ears. They will break down the way you do things and assist with building it up better.
In many disciplines our learning curve rolls over to a plateau as the years pass. Finding ways to continue to improve can be difficult. The traditional, methods of education, formal training, and self directed improvement take significant time investment.
Coaching is not training. Training is pre-constructed material. Coaching is an observation and prescriptive method for improvement.