First off what would be a benefit of crimping your barb or fishing barbless hooks? The most obvious to me is that in fly fishing it is a culture based around the beauty of a challenge between humans and fish. All the game really consists of is fooling an animal to believe what you offer is a sustainable prey and the victory of conquering that beast. I would say this is a primary focus over fishing to provide yourself food from your catch in fly fishing. Since catch and release is not intended to kill or harvest the game often the satisfaction comes from the victory over your adversary. A barbed hook is harder for a fish to be prematurely released (how embarrassing) and designed in the anglers favor especially if he intends to eat his catch. This is certainly contingent on a number of factors such as setting the hook so the it penetrates past the barb and other issues while playing the fish, jumps, head shakes, trees, corral, other anglers in the way for example.
With a barbless hook it is easier to get the hook to penetrate without the obstruction of the barb however it may be easier for the hook to come out? I am a strong believer that with a proper hook set and steadily maintained tension during the fight that a barbless hook can be to your advantage for landing a fish. There is no question that the hook will release with lack of tension and they often fall right out when the fish is in the net as the line goes slack.
Now if you are a believer in catch and release you have some level of respect for your opponent and mangling them is not high on your list of things for healthy conservation of the desired species. In Chico Fernandez book Fly Fishing for Bonefish he states that hooking a bonefish with a barbed hook upon release of the fish there is almost no chance the fish being released without harm to its mouth. On the other hand releasing a bonefish caught on a barbless hook there is almost no chance of causing harm to its mouth.
If you are a sportsman hunting for food that is fine that is not the issue here. However any hunter with a shred of ethics in them knows the sinking feeling of regret if game gets away with a non-fatal wound. If you fish for trout almost anywhere your bound to run into a fish missing a mandible or sometime both. There is nothing that bothers me more about a hero shot with a permanent smile trout gripped tightly in the center. Why disfigure an animal if you respect it enough to build a culture around the enjoyment it provides through angling and don't intend on killing and eating it.
I've had the argument also that when fishing with a large hook if you catch a smaller fish the barb may prevent the large gape from brain pinning and killing the smaller fish you will occasionally catch even when targeting big fish with big flies. You may still mangle the little guy upon release but he might have a stronger chance of survival?I guess when it comes down to it fishing is still a blood sport and occasionally casualties will occur but there are a number of things we as anglers can do to protect the fish that provide us with so much enjoyment. Crimping your barb may be a pretty good place to start.