When you create a new tab, a conversation about it will be started by default. (If you uncheck the box, you or any teammate can always start one later from within the tab.)
[Tenant Demo - show box selected in setup]
An automatic first post will appear in the channel to announce the new tab.
[Screenshot within the channel}
From within the tab, select Show tab conversation to show (or hide) the discussion, or to start one for the first time. All replies made here also show up as new replies to the original post in the channel.
[side by side screenshot]