I think that the reason the cruise lines went to the auto-tipping was because people thought that if they ate at the Lido buffet, why should they tip the dining room folks. They didn't know or chose not to know that it is the same folks doing both, just in different shifts. Plus, it used to be customary to tip the last night of the cruise and there were often some passengers rather conspicuously missing that last dinner. Pathetic attitude, in my book.
In any case, we now leave the auto-tip alone unless there is a strong reson to change it. But, if you order room service, even though it is free, it is nice to tip the person who delivers it. Anywhere from a buck for a pot of coffee to several dollars for a meal.....or big "snack".
Beyond that, it all depends on the service provided. On one HAL cruise of 16 days, I would go to this one bar before dinner for a smoke. (Yes, I'm one of those.) I never ordered a drink. Asked for ice water the first time and from then on, the bar staff would see me walk in and just bring me water. One waiter in particular treated me like royalty. Called me by name, which I never figured out since I never had reason to give him my sail and sign card. But, I went back the last night and gave one tip for them all to share and another slipped discreetly just to the one guy. They gave me an origami bird which they had all signed. I still have it, because their friendly attitude made the entire trip more pleasant.