Some rules in some areas require "single-hooked artificals only" for those reasons. That's no big problem for spin fishermen, who can replace the treble on a Mepps spinner, say, or any kind of trout spoon with a small, size 8 Siwash-style single hook. The trout don't care if they are hooked on a single-hooked lure or a single-hooked fly. The physical effect is about the same, and releasing fish will be equally easy in either case. So I think a "single-hooked" requirement is a good idea.