At one large television station I worked for, the policy was to destroy everything after two weeks. The only thing kept was the video that aired. Reporters could keep their own notes, but only on their own devices.

The news director's thinking was "they can't subpoena what we don't have."

This was in a city where the local police would subpoena at the drop of a hat, and used it as a harassment tool. The goal was to keep the subpoena storms from getting in the way of people actually reporting news.