The new Notifications API is a great way for developers to connect directly with app users and encourage reengagement by sending custom notifications about game events, invitations from friends to play games or actions users need to take in an active game. Notifications can be sent to existing users that have authorized the app; no additional or prior permission is required from users.
Facebook apps can send notifications directly to users. However, users have the ability to "turn off" notifications if desired. Image Credit: https://developers.facebook.com/
Facebook encourages developers who use the new Notifications API to use good judgment and not abuse the new feature by spamming application users:
"Notifications are a powerful way to communicate with users, but require good judgment. To ensure the best reach for your notifications, be mindful of the language you use and the frequency at which you send them."
Facebook has also provided users the means to control app notifications via an "Opt-Out" option displayed as an "X" on hover as well as the ability to report notifications by specific applications "as spam."
Developers can track the performance of app notifications in the Insights Dashboard under the Traffic / Notifications tab.
Applications are an important part of the Facebook platform and Facebook will be monitoring the Notifications API feature to ensure that "users have an optimized experience."