keeps your body in good working order...if you have a low fitness level or none..you will gain weight, lose muscle which helps support your body.....your lungs will get weak and wont be able to process oxygen as it should..your immune system will also get weak and you can get sick quicker....you dont have to be a gym rat to reap the benefits of good fitness....just fit it into your day..take the stair, walk some extra steps, take your dog for a walk..it is not only good for the body but good for the mind..