There is a lake near here that was made a C&R only lake. The reason is that it is spring fed and has virtually no winter kill. Because the trout survive the winter they grow quite large. You can go there and catch rainbows up to 6 pounds with fair sucess.
In nearby lakes of the same size and altitude it is all put and take because the winter kills are nearly 100%
C&R in winterkill lakes makes no sense to me.