It depends on the fish species, there a game fish and there are sport fish.

The easiest example is Bass. Why keep a Bass when you can go and catch Bluegills, Bream, Specks, Crappie (in most cases). Thus, releasing that Bass give it an opportunity to become a real trophy. This depends on body of water, but C&R Bass fishing has proven itself over and over again.... and they taste like *$&% compared to other species.

Trout are a very touchy subject around this area. Some people love 'em to eat, others are strictly C&R. This goes into a whole different subject of body and water and NATURAL reproduction vs. PLANTER fish.

There is a ton of information, I jsut haven't got the time to dive into it.

To each his own, if they are within legality, who gives.