On every other service I can have the photos in the cloud and not have to have them on my device. However with Photos on Mac it downloads them every time even if I turn on "optimise storage", which I thought wouldn't download them, but it does still. All I want to happen is for them to be in the cloud, and only download one by one when I want them. However right now it keeps downloading them all and filling up the SSD on the Mac too full, so my choice is to turn off iCloud Photos... which isn't a solution, or have a full SSD. This wouldn't be a problem if Apple had removable drives, but they don't.