News Web Parts
Communication Sites allow users to create News items within that site's News Web part. All Associated sites to a hub will be allowed to roll up to the hubs news web part.
If a News article is created on a specific site and rolled up to a hub with multiple audiences, the only users who will have the ability to view the news articles will be users who are a part of the specific site's audience. This means If I post a news article on the Employee Hub and because the news items roll up to the portal landing page, ONLY Employees will have the ability to view that new article.
Here is an example:
The Employee Hub will have an HR site associated with it. The Employee Hub will have a News Web part at the top of the page. The HR site will also have a news web part at the top of the page. Since the HR site is associated to the Employee Hub when a new News Article is created on the HR site and published, the news item will also be shown on the Employee Hub News web part.