YAML:

  - - "hello"

YAML expanded:

  -
    - "hello"

JSON (typical formatting):

  [
    [
      "hello"
    ]
  ]

And EDN for good measure:

  [["hello"]]

I know which one I prefer :) Silly example perhaps, but once you have X lists nested in Y lists, it does become a lot easier to see why some prefer a bit more visually hierarchically stronger syntaxes