If you're making a digital image of a car being crushed... only when it is, and will remain in future shots, cheaper to crush a physical car.
(Note that in some domains, such as video games, the cost of actually crushing the car is effectively infinite. In others, such as movies with animated talking cars, it may only be ridiculously high.)
(Note that in some domains, such as video games, the cost of actually crushing the car is effectively infinite. In others, such as movies with animated talking cars, it may only be ridiculously high.)