What is a Role and Role Hierarchy in Salesforce?

A role hierarchy works together with sharing settings to determine the levels of access users have to your Salesforce data. Users can access the data of all the users directly below them in the hierarchy. ... Each role in the hierarchy just represents a level of data access that a user or group of users needs.
The role hierarchy enables these behaviors:A manager will always have access to the same data as his or her employees, regardless of the org-wide default settings. For custom objects, you can override this behavior by deselecting the Grant Access Using Hierarchies checkbox. However, we want our role hierarchy to apply to all of our custom objects, so leave the check boxes selected.
Users who tend to need access to the same types of records can be grouped together—we’ll use these groups later when we talk about sharing rules.