Sharing to roles versus subordinates
Key Takeaway
Roles covers the users in the specified role, while Roles and Internal Subordinates also adds all of the users in roles below it.
When you share records with a role through a sharing rule, you choose whether to include just the users in that role or also everyone in the roles below it. Salesforce offers this choice as separate categories, such as Roles and Roles and Internal Subordinates. You can use them to open access to one level of the role hierarchy or to a whole branch of it.
The two dropdown lists in a sharing rule
When you define a sharing rule, you choose categories from two dropdown lists. The "Owned by members of" list sets whose records are shared, and the "Share with" list sets who gets access. You can pick role-based categories in both lists, so the choice between roles and subordinates applies on either side of the rule.