My understanding is u cannot excerpt large portions (beyond fair use) of an ND work . So e.g. u can’t republish a chapter from my PhD thesis (which is CC-BY-NC-ND) but u can republish the entire thing for free. If it were CC-BY only…you could take any parts of it and use them in an open textbook or print and distribute as many parts as u like, not the entire thing.
I assume ND for photos means u can’t edit the photo, right? but small changes like resizing – that isn’t clear to me

I think it does matter what kind of work we’re talking about. I find training materials available to online really helpful if offered CC-BY so one can reuse selected parts in one’s own training without seeking permission… But it doesn’t make sense to me for larger bodies of work. It gets complicated (incl w Conversation articles) if an article is written CC-BY-ND but photos in it are copyrighted and taken w permission. Do u copy them w/o the photos or what?