It simplifies generating JSON, since you don't need a special case for the last item, and it simplifies editing it, since you don't need to do something special when adding a new item at the end. I can't see any benefit to not having it, honestly.
> It simplifies generating JSON, since you don't need a special case for the last item
In which language can't you do array.join(",")? You can even do that in Java with one of the myriad of string libraries. I haven't hand-coded joins since (at least) six or seven years.
