If you've ever accidently deleted a file in a cloud service (or worse had someone delete a shared file) you know that any restore feature is a god send. Apple recently launched its own file restore feature for iCloud.com users that resurrects files, contacts, calendars and reminders. The new feature is buried in the Advanced area within Settings and deleted files seem to be available for restore for up to 30 days. While grabbing old files before they disappear forever is a no brainer, iCloud's restoring of calendar and contacts carries with them warnings that the restored data will overwrite the calendar and contact data currently on your devices. So you want to be careful before you start going back in time with abandon.
Calendar restore is especially touchy. If you restore a calendar all your shared calendars will have to be shared again and events will be cancelled and invitations will be resent. This is really only for when something goes horribly wrong with your calendar or contacts and you need to get back to a previous version. If you do decide to restore a calendar or contact and everything goes haywire, all is not lost. The feature grabs a snapshot of your current data and you can just restore that.