Good question Leonie. Also, great to see you in the forums still after all of these years. The quick answer is both.
The project began when I needed to consolidate years of photo/video files that were strewn across multiple devices and hard drives. Consolidate, it did. Now, I have 7 copies of every images/video in that library so it will end up shrinking to about a minimum total of about 250GB after duplicates are removed but that will be a very long time from now lol. This is surely at least contributing to the issue but I'm not entirely sure that it will alleviate either issue (space on iOS devices or slow / unresponsive photos within other apps). The iCloud Library setup looks like this...
1TB iCloud Library
--> iMac (Keep Originals)
--> Macbook Pro (Optimize Storage)
--> iPad Pro, iPad 4, iPad Mini 2, iPad Mini, iPhone 6 (Optimize Storage)
--> Apple TV4, Apple Watch
My main two purposes for iCloud Library are:
A) auto-add new photos/videos to my main library on my iMac
B) Be able to edit that library (delete photos, create albums, add faces/keywords/locations etc) from my Macbook Pro or iOS devices.
I don't so much want or need access to 95% of my photo library on any of the other devices beyond the two Macs, but I keep it on them so that when I occasionally take screenshots from iPads or photos/videos from iPhone, it automatically gets added to the iCloud library and thus, my iMac. As for viewing, I'm really only interested in the latest bunch (think Photostream). I'm discovering that B apparently isn't an option as metadata isn't synced and is subsequently isn't available on my Macbook Pro or iOS devices (along with iOS interface restrictions). Your solution to use iTunes to sync that metadata is a great one! I might use that in the future should I look in to syncing specific albums.
It does sound like referenced photos is probably a bit riskier than a second library, though a second library would still be a nightmare. If only there was a way to selectively sync certain parts of iCloud Library to your iOS devices. I think the ideal solution for me would be to:
- iMac: System library + iCloud, originals and all metadata (faces, etc) stored here.
- Macbook Pro: Optimized for space. Modify contents and metadata of iCloud Library including metadata (faces, etc).
- iPads: Only contribute to iCloud Photo Library, do not sync photos.
- iPhone 6: Contribute to iCloud Photo Library but not sync 100% of the photos in that library to the iPhone which causes lag/freezing.
After seeing this, did you have any other thoughts or am I stuck with either having 2 libraries with 2 sets of metadata for everything (which I probably won't do, it's too unmanageable) or just have a gigantic iCloud Photos Library that will forever cost me $10/mo and will chew through every last GB of space on every iOS device that I will ever own?