Sex will help get you more in shape, but unless you're really kinky you'll still have to do old-fashioned exercises such as weight training and stretching and walking to the grocery store, etc.
You do have to be careful of overtraining. Perhaps your coach isn't in as good shape as you are, or perhaps she takes part in different kinds of exercises and would be overtraining if she had more sex.
So, sex is over-rated by those who need other interests in life, and underrated by others who have other interests. It just depends on what the people involved need for their daily exercises and on the ratio of fun to effort involved. That clear it up?