Before Funpass was available, you had to fill out a card on every passenger that basically was not bad ...but very detailed. Name, address, phone number, birthday, passport number etc etc etc. This card was part of your documents. And they had to be written in. (Hubby tried to use address stickers one time..not good!)
Basically everything you entered on the computer, had to be written by hand. (on each individual) It just means less "stuff" to do once you get your documents...because where you would have been doing all that writing...it just says "funpass".
With the Funpass, you step up to the Carnival rep, hand them your passports to prove who you are, give them your credit card and it is done.
Now there are some ports that require an additional customs card be filled out before you check in. Those are mailed to you with your documents. But there are not to many ports that require that.