Previously, 14 data categories within iCloud were protected. This new feature brings that count to 23, including photos, notes, voice memos, reminders, Safari bookmarks, and iCloud backups of the contents of your devices. Not everything is encrypted in this way, though. Critically, calendar and mail are untouched here. Apple says they are not covered “because of the need to interoperate with the global email, contacts, and calendar systems.”
Good step, and something every cloud provider ought to be offering.