Earlier quoted context omitted.
I'm a dual Canadian/U.S. citizen, although I was born so in both countries (born to American parents on Canadian soil). I've never once had to worry about this whole renunciation thing. Additionally, my brother became a Canadian citizen (born U.S.), and again had no problems; Canada didn't care about his U.S. citizenship, and the U.S. doesn't care about his Canadian citizenship. He could officially renounce his U.S.…
There may be some upside to renounce a citizenship to do with avoiding extradition. But unless you plan to get involved in criminal investigations, it's probably not worth it. If America would get a draft again, could a dual citizen be drafted?
If that were to happen, there would definitely be an upside to renunciation. ;-)