iCloud Photo Sharing lets you share photos with other people and also lets them share photos with you. So, you can share experiences from an event, collaborate on a project, and all without having to individually message photos back and forth. The downside is, of course, you might discover you're not really interested in that many photos from that many people, and the notifications that go with them. In that case, you can easily remove yourself from any shared Photo Stream in just a few taps.
How to remove yourself from a shared Photo Stream on iPhone and iPad
Launch the Photos app on your iPhone or iPad.
Tap on the Shared tab in the bottom navigation.
Tap on the Sharing button in the top left to get to the main list of your streams.
Tap on the name of the stream you'd like to unsubscribe from.
Tap on People at the bottom.
Tap on Unsubscribe.
Tap Unsubscribe in the popup menu one more time to confirm.
If you ever want to be included in a particular stream again, just ask the creator to re-add you again.