Your kidneys, when you work out, make your pee as concentrated as possible to conserve water in the body but when you are not, more water is let out.
When we work out we all sweat and when we do we lose all kinds of fluids and electrolytes with it. Some of the most important electrolytes are sodium, chloride, potassium, bicarbonate, calcium, and phosphate.
Gatorade actually helps the water get absorbed faster into your body because it follows the electrolytes that are in the gatorade.
The small intestine likes to take in glucose and also pick up sodium and water so gatorade still helps there. It also helps retain water because of osmosis and salt and how it goes to where the water is which helps to keep it in the body.
In conclusion, gatorade really does help during a workout but other than that water is better because your body wouldn't need any of the extra things that gatorade packs.