It would minimize the number of roles we have to create if one user could be assigned more than one role. Example: we have a director who works in our admin department. We would want to assign FD roles as well as Admin. Currently we have to create one unique role - it would be easier to assign her BOTH roles.
+1. Creating a custom role does not help because we utilize roles for @mentions and it would cause chaos.
We have a role in our organization settings that gives the person both of those sets of access permissions at once, and it's listed as Admin/FD. Not sure if this would help your situation. Good luck!