Tippet Rings are small, very strong and lightweight, and make rigging and tippet replacement fast and easy. A leader with a tippet ring turns over perfectly, and they are light enough to use when fishing dry flies. Just tie the tippet ring to a leader with a clinch knot, and then add the required tippet in the same way. Tapered leaders last longer with a tippet ring as the leader will not be shortened every time the angler replaces the tippet. Tippet rings also make it extremely easy to add droppers, and are an excellent choice for European Style Nymphing and for Indicator nymph fishing.
I started using these about a year ago and I've been so pleased. They've saved me so much time messing around with other knots, or changing/rebuilding leaders. They're so easy to use and they really make rigging a lot easier. I'll use them for dries or for nymphing and they're great. They don't deter fish or anything, they're so small you can barely notice them but I'm always glad that they are there.
I was a late adopter of tippet rings. I had a buddy that swore by them and I just didn't like the look. I was worried that the fish may see them. It's really been a game changer for me. It keeps me honest about monitoring my tippet section. It also prevents me from cutting too much in my leader. If I am using a dropper rigs, it also allows me to pre-rig and change out the combination quickly. Get it as small as possible, but they are great. And they will make your fishing easier and your presentation better.