What is the difference between iCloud Photo Library and My Photo Stream In my iPhone settings I have both set ON. What is the difference if I turn one or the other off?i
iCloud Photo Library puts all your images in the cloud, allowing access from any device you are signed into. It requires enough space on iCloud to store all of your photos.

Photo Stream just shares your new photos with your other device, but they aren't actually in the cloud. This doesn't require you to have enough storage space for your photos.