Fiona MacDonald writes with a quandary relating to getting rid of pictures she doesn’t want:
With photos taken on my iPad or iPhone, unless I delete them from the device immediately, am I unable to get rid of them on my iMac? Now, with a less than perfect Wi-Fi signal to my new Apple TV, these same photos are taking aeons trying to load onto the Apple TV device.
This almost certainly relates to My Photo Stream (as it’s called in iOS 9 and El Captain), which works with iCloud, but is distinct and separate from iCloud Photo Library’s syncing. The fact that two interrelated options exist that seem to provide the same function has confused more people than just Fiona.
Read more here:: How to delete photos after they sync