To a point it makes sense to throw back the small ones. Walleyes that are 12 to 14 inches long give very little meat. But, at 15" they are starting to be good pan sized fish.
Walleyes and Northerns will eat their own kind but that's not the preferred food for them. As long as there's adequate forage they will go for other fish first.
The idea behind perfect management is to have a variety of sizes in the fishery. But, as far as producers, the larger fish obviously lay more eggs than do the small ones. One big female will lay more eggs than many, many smaller ones.
Plus, a large trophy sized fish is more fun to catch. Once the fun has been had, toss it back so someone else can catch it again and again.
One example I can give is that a 5 lb bass is considered a trophy in Minnesota. I fish one lake time after time and it has a good population of large fish. Lots and lots of them from 3 to 4 lbs and some getting to be 5lbs or a little better.
Interesting thing. A few years ago I caught a bass just over five pounds and the hook ripped his lips pretty good. The top right side was really torn. But, I threw it back. Last summer, my wife's young cousin caught a fish that was 6lbs 6oz. It had a ripped upper right lip. But,the boy was thrilled. His largest fish ever. He took the fish and had it mounted. He'll have that memory for the rest of his life. Had I killed it to eat, he never would have experienced it. In the mean time, that thing had two or three years to spawn and pass on it's genes in that lake. Lots and lots of babies with the potential to grow large.
That's what it's all about. No one is suggesting that you kill every single fish that's small either. Conservation dictates that you take what you need and release everything else.
It's just me. But, I really believe in it.
Randy