"Edit Users - User Roles" is what lets an admin assign a role to a user on the user-edit page (the Global User Role dropdown, and the per-location role dropdowns) — without it, those fields don't even show up, and any change is written to the role-change audit log. "Edit Users Roles" is a separate permission that lets someone open the Users Roles screen and define/edit the roles themselves — their names and which permissions they include. They're independent permissions; a role can be given one, both, or neither.