I agree that one could make wild YAML if you get into advanced stuff, but I make YAML files that look like this:

  things:
    - title: "A thing"
      item_id: "deadbeef-feb1-4e8c-b61c-dd9a7a9fffff"
      is_active: true
      favorite_formats:
        - yml
        - ini
    - title: "Another thing"
      item_id: "deadbeef-feb1-3333-4444-dd9a7a9fffff"
      is_active: false
      favorite_formats:
        - mp3
        - wav

Just because you can use it to create a monstrosity doesn't prevent it from being useful for simple configuration. Basically, it's just prettier JSON.