IBinder protocol transaction code: tell an app asynchronously that the caller likes it. The app is responsible for incrementing and maintaining its own like counter, and may display this value to the user to indicate the quality of the app. This is an optional command that applications do not need to handle, so the default implementation is to do nothing.

There is no response returned and nothing about the system will be functionally affected by it, but it will improve the app's self-esteem.

[Android Documentation]