Depends on the situation. I agree that it shouldn't just be used as a regular beverage. However, it can be very valuable when you are ill and dehydrated.

To answer the original question; yes it really does help with dehydration. It contains sodium. Sodium causes the kidneys to retain more fluid so it helps reduce fluid loss. When there is more fluid in the blood vessels, it helps maintain adequate blood pressure. The other electrolytes, ie potassium and magnesium don't help with the dehydration per se. But when you are losing fluids through sweat, diarrhea, vomiting, you lose magnesium and potassium as well, so the gatorade (or pedialyte or powerade) helps replace what you've lost