I came across this formatting pattern in Haskell, but I still prefer trailing commas for one reason: I can trivially apply line-wise operations (e.g. sort or align) on the key-value pairs without breaking the syntax. When I sort your first snippet line-by-line, it becomes

  , "age": 229
  , "appearance": "Tree-like.  It's a tree."
  , "sex": "monoecious species"
  { "time": "3 minutes past four"
  }

and the syntax is broken. With trailing commas, the syntax always stays valid:

  {
    "age": 229,
    "appearance": "Tree-like.  It's a tree.",
    "sex": "monoecious species",
    "time": "3 minutes past four",
  }