I have a nightguard because I grind my teeth when I sleep. mindways had to use one for a while for TMJ too. They're not horrible, and they're much closer to, say, the thing one wears to avoid getting one's teeth knocked in while playing lacrosse or field hockey, than the thing one wears because the orthodontist is out to get you.

I like to think of mine as nasty-lacrosse-dream prevention. Nobody's knocking my teeth in while I sleep. Including me.