To add: Exercise builds strength, including cardiovascular. Just having a low bodyfat % isn't the epitome of health, there's plenty of facets to focus on.

I have a friend with a heart condition, prior to surgery he couldn't even walk 100 ft or stand for more than a minute. He put on significant weight, partially due to lifestyle changes when his heart was failing. Now he _has_ to walk a lot to strengthen his heart again, and he's working on his diet to lose weight as a whole separate component. The walking has nothing to do with weight loss for him, it's purely about strength. I think a lot of people fail to make any kind of distinction there, and they just think of exercise as a way to lose weight.