All lies aren't useless, some can be insightful even when blatantly wrong in themselves (for instance: taken literally every scientific model is a lie). I can definitely see how an LLM hallucinating can helps fostering creativity (the same way psychedelics can), even if all they say is bullshit.
I'm using hallucination to mean "not exactly the thing", not outright lying. So maybe the "truth" is "My socks are wet." A hallucination could be "My socks are damp."