There might be some cases where it makes sense. Think about stupidly extreme sports (SES) for example. If someone organises a SES event for you, it might be reasonable for you to have an agreement that says they checked everything they could and you were informed about everything you should. But you shouldn't be able to sue them when you get hurt, since you knew from the beginning the whole thing will be dangerous. It doesn't have to be SES to apply this logic to some extent however. Every time I go kayaking on an artificial course I sign some "I'm aware this is dangerous and I want to do it anyway" papers. I'm sure those papers would be the first thing presented in court if I wanted to sue the organisers for breaking some bones. It's not giving up my rights really, but has almost the same effect in a limited scope.