If someone who is being interviewed wants to help the journalist uncover the truth about a subject but does not want to risk their job or reputation they might tell the journalist something in confidence. They do this by telling the journalist to keep this off their records of what was said in the interview. The journalist would have to abandon their own morals and integrity to tell someone where they got the information from, which might cause them to lose their job. And even then the source will probably deny that they said it. So it is hard for the journalist to print the information as they are not able to verify to others where they got the information from. So it is not as valuable as if the source was willing to go on the record. However it can help the journalist ask the right question and dig in the right places to uncover the truth through other means.