Body Mass Index (BMI) is an important health guide because it is a simple and easy way to assess a person's weight in relation to their height. It is not a perfect measure of health, but it is a good starting point for identifying people who may be at risk for certain health conditions.

However, it is important to note that BMI is just one measure of health. Other factors, such as diet, exercise, and overall lifestyle, also play a role in determining a person's health.