Business have 3rd-party services: legal team, contractor, accounting, even service providers should be able to be assigned tasks. Assigning 3rd party gives clarity to who is responsible for this, or who is completing it.
As a manager I find many tasks that rely on outside services and for clarity it would be great to assign tasks to 3rd patty. No visibility necessary, but clarity to who/what is responsible.
Tags are a find solution for now, but assigning would be best.