Eco Idle is crucial for 660cc cars as it enhances fuel efficiency and reduces emissions. This feature automatically shuts off the engine when the vehicle is stationary, such as at traffic lights or in traffic jams, and restarts it instantly when the accelerator is pressed. By minimizing fuel consumption during idle times, Eco Idle helps 660cc cars achieve better mileage, which is especially important given their smaller engine size. This not only benefits the environment by reducing carbon emissions but also lowers running costs for the owner, making it a valuable addition to fuel-efficient, compact cars.