Each of the underlined roles represents that role's view of the data. This tool is designed to save time, in that, instead of creating new criteria for each of your divisions or departments of your Organization, management can use this tool to get the different angles of analysis.
Often, there's confusion when running an Opportunity-related report, because you maybe don't see all the Opportunities you're looking to report on. So, if you click on a role in the Organization Drill Down that's higher on the hierarchy, you'll get that role's view of the Opportunities in the system.
Note: The Organization Drill Down will NOT allow users to access more information than the Organization-Wide Sharing will allow. When drilling into a higher role, the Organization Drill Down will only reveal additional opportunities if that user has ACCESS to those records in the system. So this tool is primarily used by management, or those that have salespeople reporting to them on the hierarchy.