Call NCL and request that you be "added" to the program. As far as benefits, all I have been entitled to are the Latitudes magazine and supposedly a special Latitudes line at the terminal. I really have not seen that this line is that much faster.
As for the line being much faster, well it depends on how many latitude versus none latitude members are sailing. When we arrived at the port in Miami last month we were directed to a sitting area according to our latitude level. For us it was much faster, other times, no. Other advantages, discounts and upgrades are certain sailings, laititude party on all cruises with door prizes (I never win ) and discounts in the gift shop toward the end of the cruise. Also on the Jewel there were 1/2 price nights in the specialty restaurants for latitude members only. It is like any other free program, there are advantages, but nothing earth shaking. NMNita