The reason you’d want to favorite a Playbook is to park it in its respective field so you can look at it later; preventing it from disappearing when the Playbooks refresh each week.
Within each of the “Fields,” you will see the current Playbooks being recommended for your team.
To favorite, simply tap the star in the upper right-hand corner of the Playbook tile.
And, voila! That Playbook will be parked under "Favorites" in the top right corner until you decide to unfavorite or activate the Playbook for your team's enjoyment.