Every car is different. It might make sense to buy a Prius new, but a M5 would be an opposite example. Brand new, they’re going for >$100k. 3-4 years old CPO goes for $40-60k. That’s >$40k depreciation in 3 years. If you can get it for ~$40k, there’s no way you’ll lose >$40k on the car in the next 3 years.