Motor oil in fuel

So I was approach by an retired farmer who use to have an older ford with the 6.9 diesel and asked if I was putting motor oil in my diesel when I filled up. Said it helps lube the injector pump especially these days with all this low sulfur fuels. Of course me being a green horn and still learning I said “huh”. Lol. It makes sense but what are the cons to using motor oil if any.  Thanks

You dont need to, that engine was built in the low sulfer era and will run fine without any additives.