Groups are generally set up for specific purposes of "internal collaboration"
It would be good for a Group Channel to have additional permission controls, where they could "publish" out videos to non-group members.
Maybe by default, the Group is the only one with permissions to access the Stream channel, but it could be enabled to allow external "View Only" users to see the videos without physically being a member of the Group and having access to additional tools, such as Planner, or SharePoint, or Outlook Conversations.
So in essence, the Group is for internal collaboration, and the the Stream Channel attached for the Group could become an company facing interface for video purposes.
Learning and Performance Team has a Group where they conduct internal team-based work. They use their Group Channel to publish videos to users all over the company. Instead of having 2 Groups (one for internal business and one for strictly publishing videos).
Having 2 Groups leads to duplication and confusion on where work should be posted, where conversations should be had, etc.