If you use Macs you may have heard that the new version of OS X has a system that automatically uploads all documents in your Desktop and Documents folders to iCloud. This not only gets you a backup, which is nice. It also allows you to access the files on your desktop from your iPad or iPhone or another desktop if you're not at that computer. That's awesome. I was excited to try it. I have a Mac at work, a Mac at home and then also a Mac Air for when I'm not at either place. I also have an iPad and an iPhone. All good.

So today at work I had Sierra start syncing my work Desktop and Documents folders. Later I checked in iCloud and there it all was. Awesome.

What I didn't see were my Desktop files from my home computer. That was odd because I'd upgraded to Sierra at home the night before. So why hadn't it worked from home?

<snip>

After moving a bunch of files, I tried again. Success! It let me do it. Then in a flash all the files on my desktop disappeared and were replaced by the files from my work desktop. (emphasis in original)

Arghghgghhgghgh!

<big snip>

I'll spare you all the other details. But the gist is that based on my own experience and discussing this with multiple Apple Care support folks, OS X Sierra had some major problem with syncing multiple desktops and is liable to think a second computer you try to sync is the same as the first one and try to sync over the second computer. Needless to say, that's not good. To explain everything that happened, what we figured out about where it put the data, etc., would take a post five times longer than this one. Suffice it to say, working with the Apple Care folks, I had to erase the entire computer and begin restoring my data from my Time Machine back up. (emphasis added)