s/JSON/YAML/g
    s/curly braces/whitespace/g

Well in that case, it's all the ways that IDEs like to jank up whitespace, as well as the additional difficulty knowing 'context'.

With JSON it's fairly easy for me to know if I want to end my structure as well as the structure containing it, I can just type }}, and add the next element.

With whitespace you have to keep track of HOW MUCH whitespace, and trust me once you've got people who are entirely inconsistent with how much whitespace they use it becomes a huge PITA.