Grant Access Using Hierarchies
Key Takeaway
Users in higher roles automatically get access to records owned by or shared with users below them. The Grant Access Using Hierarchies setting controls this per object, and you can disable it only for custom objects.
The role hierarchy lets users in higher roles, such as managers, automatically see and work with records owned by or shared with the users below them. The Grant Access Using Hierarchies setting controls whether this upward access applies to an object. When the setting is on, managers get visibility into their team's data without you creating sharing rules or using other features.
How the role hierarchy opens up access
The role hierarchy opens up access vertically. Users can always view and edit all data owned by or shared with users below them in the role hierarchy.
For example, imagine that the Sales Manager role sits above the Sales Rep role. Sales Managers automatically get access to all records that Sales Reps own. They also get access to all records that Sales Reps can reach through sharing rules, manual sharing or other features.
The "Managers in the Role Hierarchy" related list shows every user above you in the hierarchy. Each of those users has the same access to your data that you have.