How does the Role Hierarchy control record access?

The Role Hierarchy is a tree structure mirroring the organisation's reporting structure. Users in a higher role automatically gain access to records owned by users in roles beneath them (when OWD is not Public Read/Write and "Grant Access Using Hierarchies" is enabled). This means a Sales Manager can view all records owned by their Sales Reps. The role hierarchy does not control object-level permissions (that is done by profiles/permission sets). Custom objects have a "Grant Access Using Hierarchies" toggle — disabling it means only sharing rules/OWD control access regardless of role position.