And remember, if you are a larger drinker, that limit is 2 bottles/1 6-pack PER PERSON and PER PORT, so that can really add up over the course of a cruise. 2 adults, 4 ports (including the initial boarding), can be 8, 6-packs or 16 bottles of wine on a 7-day cruise, if you were a big drinker, that can save you hundreds of dollars.
Personally, I did it FOR the convenience. I didn't find it difficult at all to carry on. (We stopped at a store on the way to the port. It was fun to shop for what we wanted. Picked up some of our favorite soda/seltzer too.) Then, in the room we could have a glass of wine while getting ready for dinner, or a beer on the veranda in the evening, or whatever we wanted. The room steward brought us glasses (four at a time) and took the ones we used each night and replenished them as needed. We brought our own cork screw. Sure we still drank some in the bars (especially liked the Skyline!) but it was nice to have another option. Great with the free room service too!