Role hierarchy record access
Key Takeaway
Role hierarchy access flows up, not down or sideways. You can stop it by disabling Grant Access Using Hierarchies, but only for custom objects.
The role hierarchy is a tree of roles that opens up record access vertically, so managers can see their team's data without extra sharing rules. It works together with organization-wide defaults to decide what records users can access.
How access flows through the hierarchy
Users in higher roles automatically get access to records owned by or shared with their subordinates, the users in roles below them. The access they get includes what the subordinates got through sharing rules, manual sharing or other features.
Access flows up the hierarchy, not down.
For example, imagine the Sales Manager role is above the Sales Rep role. Sales Managers can view, edit and report on all records Sales Reps own or can access, and no sharing rule is needed to grant this. Access doesn't flow down, so the hierarchy doesn't give Sales Reps access to records Sales Managers own.
Access doesn't flow sideways either. Users in separate branches of the hierarchy don't see each other's data through the hierarchy, so use sharing rules to share records between groups in different branches.