In the latest versions of iOS 11 and macOS High Sierra, you now have the option of storing your iMessages in iCloud. There are two benefits. First, your messages are synced across your devices. When you delete a conversation on one device, the conversation is deleted on all your devices. Second, your older messages (and attachments) are not stored on your devices, which can save critical storage space on your iOS devices. While these are great features, keep these issues in mind before enabling Messages in iCloud:
- In the local storage model, a hacker or law enforcement would physically need your iPhone to see your messages. Alternatively, a hacker or law enforcement could get your messages in an iCloud backup of your phone. (Note the security implications of using iCloud backups of your iOS devices. I don’t backup my iOS devices in iCloud.) With messages in iCloud, your messages are theoretically easier to obtain by third parties.
- The free iCloud storage tier is only 5 GB. So large Messages databases might require a paid iCloud subscription. Go to Settings->General->iPhone Storage to see the size of your Messages database.