This allows an app's data and settings to be restored when you reinstall the app on HTC 10.
On phones running Android 8, these are the items that can be backed up using your Google Account:
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 network.
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.