I can think of an advantage of belief in a flat earth. If the earth is flat and enclosed, and there is no such thing as space, there cannot be any ET aliens. Anything that pretends to be ET aliens can only be trying to deceive us.
Once you give up the Biblical focus on the earth, and accept the earth as just another planet, it is easy to think that there are extraterrestrial aliens that are more advanced technologically and that they can come to earth and help us solve our problems. Of course, that sets up the one who thinks of earth as just another planet to be unable to tell that he is listening to what the Bible calls “devils” pretending to be ETs.