Documentaries about living public figures are generally made with their cooperation. The arrangement is a negotiation over access, and its terms are visible in the finished work if you know what to look for.
Archive material is privately held
Personal photographs, home recordings, unreleased music and behind-the-scenes footage sit in private collections controlled by the subject or their representatives.
A film without that material must rely on public footage everyone has already seen, which weakens it considerably as a piece of storytelling.
Access to the archive is therefore the main thing being traded, and it is why unauthorised films about the same subject feel comparatively thin.
Participation brings the surrounding circle
Family, collaborators and colleagues take their cue from the subject, and their willingness to be interviewed usually depends on the project being sanctioned.
Without that signal, a filmmaker is left with commentators and journalists rather than with people who were present for the events described.
The difference in testimony is substantial, and it is the second reason authorisation is pursued even by filmmakers who would prefer independence.
Approval rights are the price
Agreements commonly grant the subject some form of review, ranging from consultation on accuracy to explicit approval of the final cut.
Where approval is absolute, the film becomes a controlled account, and material that reflects badly on the subject will not survive the process.
Filmmakers negotiate to limit those rights, and the resulting compromises differ enough between projects that the credits are worth reading carefully.
Ownership shifts the incentives further
Some documentaries are produced by companies the subject controls, which removes the negotiation entirely and makes the film a self-published account.
These can still be revealing, since a subject choosing to disclose something has reasons of their own, and the disclosure is often the point of the exercise.
They should nonetheless be read as authored by the subject rather than about them, which is a different category of document.
Timing usually reveals the purpose
Authorised documentaries tend to arrive alongside a tour, an album, a comeback or a reputational difficulty that the film is positioned to address.
That coincidence is not concealed, and the release calendar is one of the clearer indicators of what the project was assembled to accomplish.
Watching with that context intact does not diminish the film, but it does place the account it offers within the circumstances that produced it.