[FaridIO]

Additionally, if you take a 4MB photo and add it to a shared album with 5 people, those 5 people all have to use up 4MB from their storage. Instead of reusing the same image and having pointers to it, it looks like it's "copied".

[carleton]

That doesn't make sense to me. Apple says here that photos in a shared album do not count against your iCloud storage.

https://support.apple.com/en-us/HT202786

[arthurmorgan]

Shared Albums don't count against your iCloud Storage.