Not understand which comment?
For mine, Carnival does not use the term 'formal night' anymore. It is either 'cruise elegant' or 'cruise casual' with relaxed requirements. Cruise Elegant means slacks and a dress shirt (no tie or jacket) is officially acceptable. Cruise Casual even allows shorts to be worn at dinner.
What Tim C is referring to is paying the airline luggage fees for carting extra clothes along for those 'cruise elegant' nights. Lots of people cruise these days with just the stuff they can fit in their carry-on luggage.