I’ve been told that in legal documents in the US, the comma is necessary. If, for example, you leave a will for $6 million, to be divided equally between four people: Paul, Jan, Joan, and Bill will each get $1.5 million. But Paul, Jan, Joan and Bill wil get $2/$2/$1/$1 million.
It was heresay information, though, and I’m prepared to be corrected.
Personally, I vote for using the comma.