Not knowing your goals or how to reach them can cause mental health symptoms. There are many reasons to control your mental state. Another good reason is to lower risk of other health conditions such as heart disease and metabolic conditions (like diabetes).
This can happen because mental health can cause people to not take care of themselves like they want or need to. It can stop or lower motivation so someone doesn't eat well, exercise or lower stress. Let's say you or somebody you care about has depression. Depression can affect motivation to eat right or exercise. This can lead to higher risk of heart disease.
Mental health matters. Better control can mean lower chance of getting other health conditions which means a better quality of life.