iCloud & iCloud Photos · iCloud Photos and the Photos library
Why is my Photos library still big with Optimize Mac Storage on?
Short answer: Photos only replaces originals with smaller versions when your Mac needs the space, and keeps recent, edited and still-uploading items full size. Confirm the setting and that uploads have finished; it shrinks as space gets tight.
Because Photos only swaps originals for smaller versions when your Mac actually needs the space, and it keeps recent photos, ones you've edited, and items still uploading at full size. With plenty of free space, the library can stay large.
Things to check:
- Photos → Settings → iCloud really says Optimize Mac Storage.
- Uploading has finished — Photos keeps originals until they're safely in iCloud.
- Big videos you imported recently, which take the most room.
There's no button to force Photos to shrink immediately. If you need space now, free it elsewhere — Storage Studio can relocate other large folders and apps to your fast drive — and Photos will rebalance as space gets tighter.