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.
Gate check will auto transfer to subsequent or connector flights. If you have more than one flight, there's always a chance that bag gets misplaced or someone makes an error. It happens all the time.