They are fairly harmless - just very, very sad. A therapist had told the husband of a schizophrenic to let her do whatever she wants. I'm interested in mold28's question. They hear something as if it is real but no one else can hear it. It is a distorted perception of reality.
Delusions are thoughts - fixed false beliefs.
Hallucinations are disturbed perceptions, delusions are distorted thoughts. It is hard to motivate or change someone with untreated schizophrenia. Often - there is not a lot one can do if the person is not interested n taking medications. Sometimes, even if they are taking medications - it may not be as effective as one would hope. Schizophrenia is a disease that also distorts a person's sense of self - of who they are and what they want.