iCloud Drive acts as a cloud-based filing cabinet. Extra storage allows you to keep large documents, PDFs, and folders synced across your Mac, iPad, and iPhone. Any change made on one device instantly reflects on the others. 4. App Data and Continuity

Generates unique, random email addresses that forward to your personal inbox to reduce spam.

In summary, buying more storage transitions your device from a standalone unit with limited space into a where your data is safe and accessible from anywhere.