It certainly can be a poor financial decision, and often is for many people. I won't argue that it's always a good decision, but there are cases where it makes sense and has benefits.
The best I could do would be to link you to this discussion, and add a few points of my own.
0% financing is generally not (I won't say never, but I've never seen it) available on used cars as it is on new cars. This automatically gives you leverage, since that money over the next five years is already beating whatever interest rate you'd be paying, as well as inflation.
The instant depreciation is indeed a negative if you're buying new cars frequently or attempting to sell soon after you buy, but amortized out over several years, it becomes pretty inconsequential.
In the case that someone isn't buying a $30,000 car (I bought a brand new 2014 Altima for $19,500 out the door, taxes and fees included) then you're looking at a smaller amount of depreciation. In my case, that's about $1,750. Being as whoever bought that brand new car is trading it in after a year, I'm assuming they're not that bright, and might be just the kind of person who would drive like a dipshit. Is $1,750 a lot of money? Sure. Is it worth it to know that some dipshit hasn't spent the last 12 months slamming on his brakes, putting in the wrong type of oil, spilling food in the car and jumping sidewalks? I haven't really thought of it, but yeah, it kinda is worth that.
Now, that's sort of a pessimistic view, and more likely than not the car will be fine. But the 0% interest, peace of mind, and ability to take car of my own car from the first minute is worth the bump in depreciation that gets less dramatic over the years.