iCloud photo library is taking up too much space on iPhone
Last week I finally got around to sorting my photos out. We have a large photo library spanning 15 years and just over 100GB. We've bought the 200GB iCloud option and collected everything into one Photos library and waited for it to upload. I then enabled iCloud photos and the "optimise iPhone storage" option on my 64GB iPhone 6. Photos all synced and takes up about 6GB on the iPhone. Brilliant.
The problem though, is with my wife's iPhone - 16GB iPhone 5s. We use the same iCloud account so that all our photos sync to all our devices. With all the other apps she uses, she does not have space for 6GB of photos. Even with the "optimise iPhone storage" option enabled, the phone tries to download scaled versions of each photo but of course runs out of space. We have also discovered that once the phone has under 300MB of available space, all iCloud Photos functionality is paused until you free up more space, and this includes uploading any photos that she takes on the phone. So my wife's photos are now not syncing to cloud, and as a result of having zero available space (60MB at the moment...) the phone runs very slowly, battery drains quickly and the photos app crashes when you try to open it.
The "optimise iPhone storage" option needs to be improved and needs to factor the available space. Either that or the user needs an option to "only download last 12 months" or something similar.