I've become a big fan of UV-cure resins in my fly tying—I would suspect that a good 75 percent of the streamers I tie incorporate the glossy, hard finish offered by these products.
But, as Tim Flagler ably demonstrates in the short video above, the hard-cure resins aren't ideal for all flies. Dry flies and nymphs that incorporate bead heads are often tied better using a more penetrating finish, like traditional head cement. These finishes simply weigh less, take up less space and help create a clean finish for flies that are meant to drift more naturally.
Check out the video. It's a good primer that'll give you some good advice on what product to use and when.
— Chris Hunt