Reb Nachman however was a great tzadik and had some amazing insights. So, in spite of some people making some mistakes, it is still very worthwhile to listen to his great lessons. For example, what he suggested about constant private prayer with God, and his way of learning quickly. And his advice about length of days which come from fear of God, which I understand to refer to learning Musar.
Even when people make mistakes, still the simple belief in a true tzadik has great value in itself.