When traveling, a funny thought I always have is watching other tourists take the same photos, from the same exact ___location, knowing it will be backed up to iCloud. I can't help but imagine how much disk space is taken up by duplicates of the exact same photo.
For a fun example, every time I'm on the Las Vegas strip I see dozens of people taking videos of the Bellagio Water Show.
There are 30 shows per night, if 50 people take videos in 4K 60fps (default on new iPhones), that's around 60 GB of data per show or ~600 TB per year of just videos of the Bellagio Fountain Show!