A PRD does not live in isolation. It is produced for people, reviewed by people, and acted on by people who each bring a different perspective and a different set of concerns. Identifying those people before you write is what ensures the document serves all of them rather than surprising some of them.
Stakeholders in a PRD process fall into three categories.
What this step requires you to do:
A PRD that surprises a key stakeholder during review is a PRD that was not ready to be written yet. This step is what prevents that.