Let's state the obvious: Having sex is fun. But what might be less obvious is that it's also good for you — mentally and physically. While it's something of a chicken or egg situation to determine the direction of causality — "Do healthier people tend to have more sex or people who have more sex tend to be healthier?" says Jennifer Bass, head of information services for the Kingsley Institute, there are some studies that link better loving with better living. Read on for the perks for getting busy.