Members – Role Hierarchy is an add-on plugin for Members. You must have it installed for this plugin to work.
The purpose of this plugin is to create a hierarchical role system. WordPress roles, by default, are not hierarchical.
Often, it makes sense that the Administrator role is higher than the Subscriber role, but that’s not how WordPress’ roles system works. It works on a simpler system: either a user/role can doing something or it cannot do something. This is problematic when you want to allow certain users to create, edit, promote, or delete other users because it means they have full access to perform these actions on any user on the install.
What this plugin does is provide a numeric system (“position”) for each role. So, you might give the Administrator role a position of 100 and the Editor role a position of 80. Then, you can allow Editors to create new users without allowing them to create new Administrators, for example.