From the American Psychological Association, "Emotional health [and wellbeing] can lead to success in work, relationships and health. In the past, researchers believed that success made people happy. Newer research reveals that it’s the other way around. Happy people are more likely to work toward goals, find the resources they need and attract others with their energy and optimism — key building blocks of success."
Emotional health is closely associated with mental health, which we know to be incredibly important in overall well-being. How well are you managing your emotions? Are your emotions overwhelming? Would you describe yourself as happy? Self-confident? Self-aware? Resilient?
Life will always bring us challenges and set backs. Having the skillets to recover from those setbacks can be incredibly important in your emotional health. Just like any other aspect of our health, mental and emotional health need attention in order to improve.