Re: Snap hooks?
Probably no negatives for streamers or large or bushy dries like hoppers.
But for delicate flies or small flies <14, I would not use them. I also wouldn't use them for any fly that is fished in the film like a spinner patterns. I question whether they would detract from emergers that depend on the no extra silhouette adding to the head.
"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy