Yes, it's a trade-off. Naturally, any time your engine is running while your vehicle is standing still, you're getting zero miles per gallon. Simply cars use a minimal corporeality of fuel when idling. Letting the engine warm up for a few minutes ways that the car will operate more than efficiently when you practice start driving. Moreover, beingness comfortable and relaxed while driving will make yous more than attentive, which makes you a safer driver.