There's a great scene in the movie 'Lady Bird' where this happens. It's not a spoiler, so don't worry. It happens right at the beginning and she does it just to prove a point. There's nothing cooler than jumping out of a moving car like that. It's the ultimate "I don't give a crap move." That's not the only time to use this move though. You might actually need it to survive.
If your brakes go out, or you're being kidnapped in a car, you may need to jump out of the car. The car won't be slowing down anytime soon, so sooner is better than later. Wouldn't you rather jump out of a car than hurl off of a cliff? Or even worse, get taken to a weird sex dungeon? Either could be your fate if you don't learn this skill.