I would partly agree that in something like "Have you ever been to Australia?", the "ever" isn't really necessary because "Have you been to Australia?" would carry the same meaning and result in the same answer. However, when talking about the future (for example), it can be useful. If someone said they didn't eat avocados and I asked "OK, but would you ever eat one?", the use of "ever" would make it clear that I'm asking whether they can imagine any point, no matter how far in the future, that they would eat one.