The biggest is not having to claim a refund when order cancelled.
As I said to BritManToo, to whom I originally responded, apart from not having to pay up front, what are the other "serious advantages" (his claim) of COD? You pointed out an advantage of not having to pay up front, not one of the other additional benefits. As I see it, there is only one advantage of COD and that's not having to pay up front.