I don't see how they could alter flight, as they are pretty much weightless, and too soft to matter if they hit the shelf. If your arrow is hitting the shelf, you have other tuning or form issues.
Yes, they help you see your arrow in flight better. I can see how they would help you find an arrow better too, especially if your fletching is in subdued colors. Another thing I do to help locate arrows is add a strip of reflective tape or wrap somewhere on your cresting. I use reflective wraps on my hunting arrows, and just a 1/2" strip on practice arrows. After dark they really jump out at you when a light even gets close. It just might help recover a Deer someday, who knows, and it can't hurt.
Mine look very full and puffy, the way I like them, because I use the 1/4" Rabbit strips for fly-tying. I spiral them around the end of the arrow, about two turns around. It takes about 3/4" of space between the fletching and the nock. I use adhesive wraps, and rough that area just a little before I apply the contact cement, and clean with rubbing alcohol. I don't have any problems with them staying put.