Roflnadal

Once a portfolio has been immunized, no more action is needed from the portfolio manager. The only relevant cash flow at that point is the one at horizon date.

CF matching, on the other hand, is more costly and harder to maintain. Coupons have to be constantly reinvested and used (along with principal of other maturing bonds) to pay down liabilities as they come due. It's easier to understand but it's not easier to maintain.