Sarah Perez:

Messages in iCloud was first announced a year ago at WWDC 2017 as a way of keeping conversations up-to-date across all your Apple devices, including iPhone, iPad, Apple Watch and Mac. Its introduction means you’ll now be able to access your entire Messages history when you set up a new Apple device, and, when you delete a message from one device, that change syncs to all your devices.

Storing messages in iCloud should help clear up loads of space on device.

More importantly, this highly-sensitive data appears to be stored securely, ensuring that no one—including Apple—can access this data.

The messages are also end-to-end encrypted for security purposes. They’re protected with a key derived from information unique to the device, combined with the device passcode – which only the device owner should know. That means no one else could access or read the data.