At what point should you start thinking about hiring a chess coach?

In my opinion there are 2 points where one should hire a chess coach.

1. For Rapid Improvment : If you are a self learner and you study books, solve tactics, play tournaments then you will definetly get the results. But a chess coach will help you to guide what to study, when to study and how to study at certain level. For Example if you are a 1500 fide Rated player and you want to reach to the 1800 rating. It might take 2 years to reach on that level but a chess coach can help you to achive this goal within 7-8 Months. 

2. To Breakthrough : Many Players stuck on certain rating level they try hard study chess 6-8 Hours in a day but can't cross the rating barrier. In Such kind of situation having a chess coach is very important. Chess coach will help you to change your playing style to reach on certain level. He/she will guide you when and what kind of tournament you should participate and how to breakthrough your rating barrier.