You ever have your whole trip get fucked up because you checked your bag and they lost it? I have.
Also, by queuing up like that, you get dibs on limited overhead luggage space - 15 minutes in a queue is 30-45 minutes you don't have to wait waiting for your baggage to arrive in Baggage Claim because you decided to not be one of those losers waiting for "reserved seats".
It's a good travel strategy to save time and energy later.