If NCL is like most of the other lines, if you have the automatic tips removed, the steward and waiters will have to turn in any money you give directly to the common pool. If you use the automatic tips, they can keep any extra money you give them.
I have been on 22 cruises on various lines and have always had great service. I consider the $10 a day a fantastic bargain and usually give a bit extra.
It is my understanding that the stewards and waiters receive only $50 per month from the cruise line and work primarily for tips. People who refuse to tip do nothing to change the mode of operation of the cruise lines. Rather, they only hurt the hard working (70 hours or more a week) people who serve them.
I would not hesitate to call anyone who refuses to tip a cheapskate.
It will not matter if you tip the person directly or leave the auto tip on your account...all monies go to the "POOL" then divied up from there.
You can of course tip extra and the waiters will get to keep the money but that is only if the auto tip is left on.
I found most cruiselines with the auto tip policy I still had good service....there is always a chance the passenger will remove the tips so the staff still work hard to please you.