I think the crawls do set the mood for the audience. They tell the viewer that what they’re watching isn’t going to be just another action movie, but something grand and operatic (though that feeling has diminished with the films after the OT). Also, they help enable that more “in medias res” form of storytelling that can throw the viewer right into the action without being confused by the time jump between films. Though I’d argue that some of the films (namely RotJ and TLJ, and possibly ESB) don’t need the crawls and would be perfectly understandable without them.