The "Optimize Mac Storage" functionality you're referring to is not enabled by default.
You can manage settings for this and other storage optimization features in About this Mac -> Storage -> Manage, and System Preferences -> iCloud -> Option... (beside iCloud Drive).
Apple does not make this clear on their Sierra micro-site, and acts as if it either enables by default, or asks you with their typical confusing dialogs to enable it when low on space (which most users would get confused and click enable).
Can you elaborate on this? Is OSX deleting iCloud documents if you run out of space?
Re:MacOS Sierra
by FireBeyond on Tuesday September 20, 2016 @04:03PM
(#12542861)
No, it deletes documents off your computer and puts them in the cloud.
If you subsequently stop paying for iCloud, you risk losing them. Or having to pay to restore them.
Yeah, it's opt-in and somewhat "implied", but I think the OP is saying there really should be an "* if you use this feature, an active iCloud subscription is required"
Like, this is class action material imho. You can't just take people's files and lock them behind a paywall just because they previously opted into the paywall on a case by case basis.
Edit: For those downvoting, it doesn't change the fact that Apple is turning file deletion on by default. This is not a good idea, especially when most of the world and part of the US still has pretty shitty Internet, or people have Internet caps.
Apple fanboyism helps no one.