I think it got covered a bit in the comments here: http://boffosocko.com/2017/07/11/the-facebook-algorithm-mom-problem/#comment-35378

In short, Facebook’s privacy settings aren’t solid enough to do a post that is “Public except X, Y, Z” so you’re forced to do “Friends except X, Y, Z” temporarily before switching to “Public” at a later time. I generally wouldn’t recommend trying to game the system like this however unless you’re experiencing this particular problem to an extreme like I was. Facebook’s shifting black box algorithm regularly changes and trying to game it is typically more time and effort than it’s worth.