I'm pretty certain that is supposed to work. Printing out your documents once is enough, yet some like to take a back-up copy, or misplace the first, so that's why the option continues to be there.
In any case, I printed mine this morning and this is what I received:
Cruise summary details (1 page)
Cruise ticket (2 pages, one to be presented for passage, one guest copy)
Excursion and itinerary (1 page for us, may be longer for longer cruises)
NCL guest ticket contract (6 pages)
Plus, separate link to luggage tag.
If you got something similar, you should be all set.