A role hierarchy represents a level of data access that a user or group of users needs. The role hierarchy ensures that managers always have access to the same data as their employees, regardless of the organization-wide default settings. Role hierarchies don't have to match your organization chart exactly. Instead, each role in the hierarchy should represent a level of data access that a user or group of users needs.
Control Access to Records - Trailhead - https://trailhead.salesforce.com/en/content/learn/modules/data_security/data_security_records