Honestly, nothing. Except the endless debate on where the braces go, and how long they're allowed to stay on a single line.

It seems trivial, but replacing scope delimiters with a per-line signifier (i.e. indent) makes the scope of each line self-contained and sidesteps that discussion.

Is that worth YAYAML (Yet another YAML)? I don't know. But I certainly get the desire to skip the discussion :)

But it can't be minified without keeping the line endings and whitespace, unlike JSON.