What does "Backup my Data" really do?

[wmscottmc]

Im not sure if this is a new feature or not. But in settings/privacy there is a "backup my data" app. I dont have mine checked.

Just wondering, what does it backup, and to where?

Do most users leave this option checked, and if so are backups performed automatically? Is the data that apps used backed up, or just the app?

Thanks