What does Unpublishing Segment Emails Actually Do?

What does unpublishing a segment email actually do? There’s no documentation for it.

Until a segment email is unpublished, you can’t send it out or it cannot be timed for future send.
Once you publish and email and a sending window is described
Then the segment members will start getting this email. If someone becomes a member of the segment within the sending window, they will recieve the email. In other words, anyone who falls into the segment and the ‘window is open’, will ge the email.
If the email is unpublished, this mechanism is off.