I’m not sure exactly when this happened, possibly with updating to Sierra, possible during one of the security updates to OSX that took place over the last couple of months, but you want to double check your iCloud settings on all of your iMacs and Macbooks. I didn’t find this out until I suddenly got a warning that I was running out of capacity on my iCloud drive.
I had disabled all automatic storage and backup from from my iMac to my iCloud account because I don’t need it except for photo sharing. I do my own backups to external devices so I didn’t need it for that. I also didn’t want documents, emails or other information being stored off-line out in the cloud because I don’t particularly want things like financial information, tax returns and similar information stored heaven only knows where on some server I have no control over.
Somewhere along the way, perhaps with the upgrade to Sierra, Apple decided to reset all of my iCloud preferences and now everything was turned on. It was automatically saving my entire documents folder, desktop files, contact lists, calendar, and pretty much everything out on the iCloud. Even worse, it had also turned on iCloud for every third party application that has iCloud capabilities – word processors, accounting software, a couple of photo editors — all of them were now storing duplicates of everything out on the cloud as well as on my local drives.
Not only is this a privacy concern, it also sucked up a hell of a lot of storage space, and while iCloud storage isn’t exactly expensive, it still costs money.
So if you use iMacs or Macbook computers, go to your system preferences and check your iCloud preferences so you know what’s actually being stored out on the cloud somewhere.
Important – just found out the hard way that if you do disable Sierra’s ability to “share” your documents and desktop with iCloud, and then delete the documents and desktop folders on your iCloud account, it will also delete the documents folder and any documents, photos, etc you have on your desktop from your iMac’s local hard drive as well.
And, of course, I’d emptied the trash bin before I found this out and had to restore my documents folder from backup (Thank you Time Machine)
Additional note: Apparently just switching iCloud functions off doesn’t actually do anything. After switching it off, deleting the unwanted files from the cloud, I discovered OSX put them right back again. I had to log out of my iCloud account, reboot the computer, then log back in before the changes actually went into effect.