According to Facebook, “Scheduling a live video makes it easier to build anticipation and buzz with your audience before your broadcast begins, so you can start strong with an audience already assembled. When you schedule a live video, an announcement post will be published to News Feed letting your fans on Facebook know that the broadcast is coming.”
In addition those who can see the post can also opt to receive a one-time reminder notification when the event is about to begin. They can then join a pre-broadcast lobby in which they can interact with other users who are also waiting for the event to start, kind of like if you were at an event in person.
Before you get too excited, note that this feature is only available for Verified Pages right now. However given that Facebook Live also used to be limited to “celebrities” before opening up to the public, we can only imagine that this feature will also eventually be available for everyone else.