Radio Question: Publish Button?

In the three-button setup for Radio, the three buttons are Post, Publish, and Post & Publish.
I get what Post does. It saves the draft without putting it on the Web.
I get what Post & Publish does. It both puts the new entry on your local server and schedules it to upstream to the public server.
But what does Publish do? When would you want to publish but not post an entry? If it’s just for publishing entries that were formerly only posted, what difference is there between using Publish and using Post & Publish?