I see this mostly in perch fishing, when people are keeping 15 + Perch and they just throw them aside all flapping around on the ice or in a bucket, it just doesn't sit well with me, a good whack over the head takes no time at all, and when cleaning the fish they don't flop all over the cutting board.
I fish because I love the sport, when I don't catch and release I treat the animal with the most respect, I waste nothing and appreciate it with respect and dignity.