Facebook's newest feature just got rolled out to all pages. Understanding that all content is not equal, Facebook had previously provided Interest based targeting (in ads only) allowing users to search for audiences based on keywords. While this was good, the catch was that it could be only be used with Facebook ads and not organically.
Audience Optimization has three main features:
Audience restrictions [same as post/newsfeed targeting]
Let's talk about the first one, Preferred audiences. The main difference here is that Facebook will prioritize post delivery to those users whose interests match the post's preferred audience rules, without limiting the overall post reach.
As organic reach continues to diminish, smaller pages (businesses) contemplating moving to Facebook ads can now get data about how to route their organic content (previously unavailable) before testing the waters with Facebook ads. The post insights report from the page should probably follow in terms of adding a new column containing interest names used in post targeting (it already has languages and countries targeted).
As pages begin to understand which audiences are reacting to their organic content, they'd be more willing to jump in with Facebook ads - knowing whom to target, getting more value of their limited budgets.
Here's a screenshot of trying to use 'Baseball' as an Interest while creating a post. What's different so far is that the potential audience size is not available here. This is something that was for Interest targeting in FB Ads - giving advertisers a good idea about whether a particular interest segment is too small to warrant an ad set (or if multiple interests need to be combined to create a more feasible audience size).
Edit: Just checked this feature again. The audience size shows up after you add the interest...not while you're deciding which interest to add.
As the objective of Preferred Audience targeting is to help direct posts to the right audiences, audience sizes would probably be shown - bringing more clarity into where to direct posts.
The more (organic) audience insights Facebook shares with page owners, the more likely they are to start advertising there.
I'm yet to test posts using this targeting but it'll be cool to check back in a few weeks on what data can we find in the post itself / data downloads taken from Facebook Insights. Thread to be updated.