If a biography is authorized, then you can interview the subject, and in some cases those interviews provide a lot of the material. Walter Isaacson's biography of Steve Jobs was like this, for example.

In addition to the direct interview, there are other advantages of authorization that often allow the author a much deeper access to research the subject:

- Access to records, correspondence, and journals in the subject's possession

- explicit endorsement from the subject encourages their family, friends and colleagues to work with the author.

- Opportunities for the subject themselves to fact-check and contextualize the research.

That must be balanced against the fact that authorization also often provides the subject an opportunity to review the content, giving them a hand in crafting the narrative and/or suppressing unflattering details.