I think it depends on the fishery and abundance of aquatic life. In most of our Southern Appalachian freestone streams trout, particularly rainbow and brook trout don't get very big because of limited food and their short life spans. In those streams, the trout will not get much bigger regardless of C&R. In fact, you may see larger fish if some of the trout are removed.
In more fertile fisheries C&R or a slot limit make perfect sense as the trout can grow to larger sizes over time and there you will benefit from the genetics of the larger fish.