Here's what can be backed up:
This allows an app's data and settings to be restored when you reinstall the app on another phone.
Auto Backup periodically backs up your phone to a private folder in Google Drive. It
occurs every 24 hours when the phone is idle, charging ,
and connected to a Wi-Fi
Backup data will not count towards your Google Drive storage quota. Large files or files that app developers have chosen to exclude from the service will not be backed up.