If you don't know, ZM, then perhaps you are doing it too ...
Imagine the poor celeb who is shooting a nude scene the next day. They think they have a spot on their backside but they can't get a good view in the hotel's bathroom mirror. They take a close up photo using their iPhone. Next thing they know, their backside is all over the internet ... because their iPhone automatically published ("backed up") their photo to their iCloud account, which had been hacked.
With your "friends", it doesn't have to be hacked. You can share iCloud access with who you like ...
https://support.apple.com/en-gb/HT202786
... and, months later, forget that you've done so when taking your own intimate photos and videos, for whatever reason.