How iCloud Backup works
iCloud helps keep your data safe in two main ways: syncing and backing up. For example, if you're using iCloud Photos, iCloud Drive, or Notes, your information automatically syncs to the cloud and is kept up-to-date across all of your devices whenever you make a change.
Any data on your device that isn't regularly synced is stored in your iCloud Backup. With Backup turned on, iCloud takes periodic snapshots of this data to make sure that it's easy to restore any time you get a new device.
Between syncing and backing up, all of your data is kept safe in the cloud.
What iCloud Backup includes
Your iPhone and iPad backups include all the information and settings stored on your device that don't already sync to iCloud.
Device settings, Home Screen layout, and app organization
When you restore from an iCloud backup, things like your device settings, your Home Screen layout, and app organization are also restored.
Other on-device information
Any purchased Ringtones and your Visual Voicemail password (which requires the SIM card that was in use during backup) are also included in your iCloud Backup.
Apple Watch backups
Your Apple Watch backup is included in the backup of your iPhone or iPad.
Photos, videos, messages, and app data
If you don't use services like Messages in iCloud or iCloud Photos, the information below is stored in your iCloud Backup to ensure that it's also protected.
iMessage, text (SMS), and MMS messages
If you haven't turned on Messages in iCloud, your messages are included in iCloud Backup. If you use Messages in iCloud, your messages automatically sync to iCloud so they aren’t included in your daily backup.
Photos and videos on your iPhone or iPad
If you haven’t turned on iCloud Photos, iCloud Backup may include photos and videos in your Photos or Camera Roll, as well as face information from the People & Pets album. When you use iCloud Photos, your photos, videos, and face information automatically sync to iCloud so they aren’t included in your daily backup.
iCloud Backup includes app data for the apps that you've downloaded on your device. This includes data for third-party social media apps, games, and messaging apps, as well as apps from Apple that don't sync with iCloud.
If the app uses iCloud Drive to store data, that information is stored in iCloud instead of your iCloud Backup.
How to manage your iCloud backups
If you want to reduce the size of your iCloud Backup, you can stop backing up apps that you don't use anymore, or delete old iCloud backups.