I hope I'm not missing something, but am I understanding it correctly: Messages between two people are publicly viewable, and then it's possible for other peopl

I hope I'm not missing something, but am I understanding it correctly: Messages between two people are publicly viewable, and then it's possible for other people to comment on them? I'm having a hard time wrapping my head around a general use case then. It seems like a neat idea for discussions or debates between two people which have public value.. but most of the time when I'm writing directly to someone, why would I want to have it shared? Looking at other social networks, most of the time you want to share something with your social circle and generate a conversation which has more than two people or you message them directly. Am I missing something?