I have been told that registered on-line, with the FunPass, is fairly important.
I mentioned to an agent one time that one of the Carnival cruises we booked, our documents/package didn't arrive until just a few days before we left home to fly to the port, and my brother-in-law got his doc/pkg. for the same cruise the DAY BEFORE we left. We found that very stressful. The agent said that as long as we'd filled out the FunPass, we should never stress about the doc/pkg., everything is then "in the system" (whatever that means! *L*) and even if the doc/pkg. doesn't arrive before we leave, we'll still be able to get processed and boarded.
Mind you, we register our FunPass, have our document/package and every possible bit of paper or identification we may possibly need, in our hot little hands. We never want to take chances!!! :-)