It's available on iOS, Android, Web, desktop apps and devices such as Smart TVs and Internet of Things objects. Facebook Login enables two scenarios, authentication and asking for permissions to access people's data. You can use Facebook Login simply for authentication or for both authentication and data access.

Facebook Login is used to enable the following experiences:

Account Creation
Facebook Login lets people quickly and easily create an account in your app without having to set (and likely later forget) a password. This simple and convenient experience leads to higher conversion. Once someone has created an account on one platform, they can log into your app—often with a single click—on all your other platforms. A validated email address means you're able to reach that person to re-engage them at a later date.

Personalization
Personalized experiences are more engaging and lead to higher retention. Facebook Login lets you access information which would be complex or arduous to collect via your own registration form. Even just importing someone's profile picture from Facebook gives them a stronger sense of connection with your app.