errors: [ ],
message: "SMS Successfully Queued",
The same string in XML could look like this:
<?xml version="1.0" encoding="UTF-8" ?>
<message>SMS Successfully Queued</message>
XML supports various other extras that could end up making the file containing the data much bigger. In this specific case the size difference isn't that much, but this can become much more noticeable if the data becomes more. That is why JSON is a bit more lightweight.