Does Photos Optimize Storage work differently between Mac, iPad, and iPhone?

I am using five Macs with iCloud Photos. When you import new photos, they will get uploaded to iCloud Photos.

You will be seeing the progress of the upload in the status bar, below the "All Photos" tab. See: Check the status of your library in Photos for macOS - Apple Support Is the status bar indicating any problems?

You can also check on your iCloud webpage at www.icloud.com in the Photos.app there, if your photos have already made it into iCloud. even, if you are just uploading 5GB of new photos, the upload may be taking more than a day. because Photos is not just transferring the photos, but is merging them into the existing iCloud Photos Library,

With iCloud Photos your photos will be stored in iCloud in the full resolution - iCloud Photos will be the primary storage, used for syncing the updated versions between your devices, when you are working with the photos (or videos). Each device will keep local shadow copies of the iCloud photos. As long as you do not enable "Optimize Storage", the local library will be a full copy of the library in iCloud, with all originals in the full resolution. This is perfect, if we do not always have a fast and reliable internet connection. And it is easy to make backups of our Photos Library, as Time Machine can can backup the library. That is the reason why I am not using "Optimize Mac Storage" on all my Macs, only on the Mac with the least storage. On that Mac the local copy of the Photos Library has a size of 20% of the library in iCloud.

With "Optimize Storage" turned on, iCloud Photos may be removing some of the originals, and keep only smaller, optimized versions for browsing. How many photos will become optimized, will depend on the available storage on your device, and how much storage will be be needed for the optimized versions will depend on the size and resolution of the display on your device.

As OT already explained, the optimization is fully automatic. It will kick in, when more free storage is needed, but it will not remove all originals needlessly. This way, we do not have to download the same originals over and over again. Photos will try to keep the most recently used photos stored locally, just in case we need the again. YOu may be seeing different results on each device.

If you want to force the full optimization immediately, try the procedure described here: How to force Photos for Mac to Optimise the Storage Immediately. But I would only do it, if you are desperate to free a lot of storage at once.

But how have you checked the storage used by Photos? Did you look at the Storage display in the  menu > About this Mac? Or did you check the size of the Photos Library in the Finder? Both methods will not show you the true amount of storage for the photos instantly. It may take a while, until the data will be updated.

On the Mac optimization doesn't kick in until there's about 20% free space remaining as I recall.

This is what user léonie says about how it works on an iPhone:

"When you fill your iPhone with other data will Photos remove more and more originals and replace them with smaller, optimized versions. You cannot get the photos off the iPhone completely. As an estimate - you can expect the optimization to reduce the amount of local storage for your photos on the iPhone down to 10% to 20%  of the size in iCloud. For example, if your  photos are taking up 500GB in iCloud, the optimized versions will still need 50GB to 100GB on your iPhone. How much storage are your photos taking up in iCloud?"

IMO, she's the most knowledgeable person here regarding the use if iCloud Libraries and optimization.

I don't use iCloud Library so my info is second hand.

Does the Mac Photos app import full resolution photos from iPhone when photos are optimized on the iPhone? I want an archive of photos on my own backup that is full resolution. I'm afraid that for years I've only been importing optimized versions and backing those up instead of the full version. I don't want to rely on iCloud Photos for backup and restoration of files, plus it isn't really an archive since deleting from any device deletes it from all. I didn't turn on the optimization on my iPhone, but it is on for some reason. I've always made sure my phone has plenty of storage to avoid optimization. Sadly, I only recently noticed that it is set to optimize.

Thanks.

BT123, if your Mac tries to import a photo directly from an iPhone and finds only an optimized copy, it may not import anything useful at all. You should allow the Mac to download a full resolution photo from iCloud Photos without optimization to allow the archive you desire.