When I encounter one in fiction, I know that the author is going to try to “reveal” something about a character without doing any of the heavy lifting that real plotting and character development and dialogue require. The more “structured” the dream is, the worse it is.
Dreams are, by definition, exposition. They’re telling, not showing. At the very least, they’re a narrative crutch for writers who can’t see their way forward in the plot. When a writer clears the stage of real incident and relationship and cause-and-effect, and starts editorializing about a character’s inner life by using brain-chemical shadow play, I’ll start skipping ahead. Tell me what’s really happening, I’ll say, not some free-associational aside functioning as a story-telling convenience.