Well, it's obvious that you (and LarryHN) have confirmed my suspicions. I have little to no knowledge of iCloud Drive and the iCloud Photo Library.
Now that I have more, perhaps I can phrase a better question.
On my Mac in System Preference > iCloud > Photos > Options ...
If I uncheck iCloud Photo Library, the my photos won't automatically upload to the iCloud Photo Library.
Is this an all or nothing choice?
I either upload all the photos in the Photos App, or non at all?
If I don't upload all, does that mean that no iDevice will be able to see any photo?
Or can I tell Photos to do something like only share albums?
Isn't the opposite of automatically, manually?
Maybe some background info would help. (or this post is getting too long)
About an hour after I gained a rather comprehensive understanding of Aperture, Apple announced it's (slow) end of life. At least it was a really awesome hour. For what I did/do with Aperture, Photos isn't really a replacement. But Photos appears to be the only way to share photos in the Apple ecosystem. So it looks like I will use Photos for what I want to share and keep synced across my too many Apple devices. While I use a non-Apple product to replace Aperture.
So as I try to decide how to use Photos, I'm trying to understand how Photos manages all the media. It sounds like that in order to share/sync, it's an all or nothing deal. Which is disappointing, since in my initial testing I already ran into the "you're out of storage" wall. 5GB isn't really a wall, it's more like small speed bump. I don't mind paying for things I need, unless someone else decides I have to have it.
To end on a positive note. As someone who was only tech support for my family of iPhoto users, it looks like Photos is a better app/system.
Okay I couldn't do it. (end positive) Am I the only one who wonders why they called the App Photos? Really? After all that Master, Version, Project fun stuff, they choose Photos? Who's photos? My photos, or Apples Photos? I have photo issues with my photos in photos. Sure makes for fun posting about photos.
If you've made it this far in my post, thanks.