Discuss #Office365Groups - Public or Private?

I look forward to people's experience with this and will kick this off with a question.  I fully understand private groups and many use cases for them.  I am struggling with where a public group would be appropriate.  If it is a discussion, then I think a public Yammer group would be appropriate.  I guess where I have a hard time seeing it is around file sharing.  Since members of the group have access to upload and edit files within the group what would be the use case where you would want just anyone putting files and potential editing other people's files in a group setting?  Who would be responsible for sorting out the ROT (Redundant, Obsolete, Trivial)?

What I do see is a use case for a private group who then makes their document library read only to the public, but that is not the same as a public group.

I am probably missing an obvious use case, but...