They predict long term outcome. They are the classic symptom of schizophrenia. Voices are often insulting and frightening. Almost everyone has seen someone in dirty clothes, homeless, on a street corner talking to the wind, maybe shaking their fist at the sky. It's included here because of the similarities between the negative symptoms of Schizophrenia and Depression.
Most people benefit from medication now.
With medication the individual can live in the community. Often drug and alcohol abuse predate the first episode and exacerbate symptoms. For a long time nobody wanted to work with those people. The addiction people wouldn't take them and the psychiatric hospitals wouldn't take them. Fifty per cent of the people diagnosed with schizophrenia either don't know or refuse to believe they have a treatable illness.