What's the use of knowledge of optical illusions? So that you know that "seeing is believing" is not 100% dependable. Also you just listed their "use" in your

What's the use of knowledge of optical illusions? So that you know that "seeing is believing" is not 100% dependable. Also you just listed their "use" in your very comment. People build upon these to convince others, and if you would like to be less manipulated, then they are useful to know.