Stretching warms your muscles. When you are pursuing strength training, you work the muscles against progressive resistance or overload. This was a common occurrence in medieval times when the body rack was used as a torture device. When you exercise, the water that you lose through sweating comes from recycled urine. Exercise reduces the risk of endometrial cancer and breast cancer by reducing body fat.
Body fat produces estrogen, which aids in the growth of some female cancers.
The area in which you store your fat is probably as important as the amount that you store. People who store fat around their bellybutton area are at greater risk for certain diseases than people who store fat below the waistline. The point at which energy production switches from being aerobic to anaerobic. When your aerobics' teacher gets a bit too chirpy and suddenly you find yourself wishing you'd taken up meditation instead. When your adrenaline kicks in and your energy seems to suddenly increase.