Why can dreamlike settings be powerful in literature and film?

I think that dreamlike settings can be very powerful in literature and film. It allows the author to just let all of their ideas just flow out of their mind perfectly the way he/she wants them to. The story could end anyway they want it to and the number of ideas for the story are limitless. And sometimes, a good author needs a good free write and just let everything flow out and put it on paper.