I always think that a dream sequence in a novel is a cop-out. Literary dreams hold up the narrative, are often irrelevant, and are usually rather boring. Take this, for example:
Woman lost in London. She's meant to be at a concert with her husband, but has lost him. She's forgotten where she lives, and has only keys and about two pounds in her pocket. It's dark. She's crying. She meets her neighbour, and asks where she (they) lives. "January," says the neighbour sharply. "But I asked for the address!" "January!" the neighbour repeats.
That's it. End of dream.
Are you bored yet? I am. And it was my dream. Last night. John had a much more interesting one about three men ("who might or might not have been triplets") who were all thriller-writers. That's a bit more like it. But even that would badly interrupt any story, wouldn't it? I think people put dreams into novels to play for time, or to entertain themselves.
(My most interesting dream was many years ago, and I dreamt that I was collecting jockstraps. That's right. Jockstraps. Including a Jamaican wrestler's jockstrap. I dread to think what that said about me.)