Like when you send a .7z instead of a .zip or .rar to a friend or a teacher because that's what your computer has installed and they're like "Oh No, not one of those, now I have to install 7Zip" even though the same program that opens .rar also opens .7z I feel like people are way more annoyed when they receive a .7z
It was usually split into chunks because the upload websites only allowed files of certain sizes. Like 100MB or something.
Ah you're right, completely forgot about those. They were absolutely dreadful to use.