The Sport mode keeps the transmission in gear longer and provides better throttle response. The Grand Cherokee in its Normal mode is tuned more for a comfortable ride than for athletic moves. But Sport mode is now available across the lineup, engaged with a pull on the transmission handle. In Grand Cherokees equipped with the air suspension, Sport mode wakes up the truck and transforms it significantly, changing shift patterns, suspension settings and ride height to minimize body roll and create a more surefooted performance in fast twisties. In models without the air suspension, only the transmission behavior and throttle response change.
So it should be used when you want to partake in some more spirited driving.