When you trade-in you don't have to worry about selling the vehicle yourself or any of the associated costs (advertising, showing the car, etc). A dealer may offer a price you could not get yourself as an incentive to purchase a new vehicle. If the trade-in has known problems that could plague you later (when the buyer returns complaining), selling the car to the dealer eliminates the bother. Trading-in a lease car may relieve you of, in the long run, monthly costs you cannot afford. Sometimes people trade in lease vehicles because of poor gas mileage or lack of practicality.
