When assigning a large number of records to a single user, as in the case of routing unassigned accounts for manual review, it's best to place that user at the lowest level of the role hierarchy. This configuration ensures that the user has access only to records they directly manage or need to review, minimizing unnecessary data visibility and reducing security risks. Placing the user at the lowest level in the hierarchy helps maintain data integrity and provides clear lines of record ownership.
For additional guidance on role hierarchy best practices, see: Salesforce Role Hierarchy and Sharing.