I've found it handy for storing configuration data.

E.g. user preferences

    preferences = { 
      "notifications": {
        "email": true, 
        "sms": false 
      },
      "stay_signed_in": true,
      "editor_plugin": {
        "indent_level": 2,
        "autosave": false
      }
    }

It's structured, adhoc, and "less likely" to be queried against. Of course you could implement this in normalized tables, but it's a pain, and I don't see any real value in this case.