Visibility of issue comments
Comments are private between organizations. For example, if the Builder assigns a defect to their Subcontractor, they can see comments made directly with each other on that defect. If the Builder shares all their defects with the Client, the Client cannot see any of the comments made directly between the Builder and the Subcontractor.
If you want a comment to be visible to all organizations involved with the issue, you can add a public comment. Then, when you share public comments with additional organizations, they can see all public comments that have been added to your issues.
So in the above example, if the Subcontractor raises a public comment on the Builder's issue, the Builder can share all public comments with the Client to allow them to see the Subcontractor's public comment.