I was shocked to see that some cruise lines actually leave from NY in December. Has anyone ever done this?

The last cruise I went on (in the summer a few years ago) was from NY, and I loved the convenience of it. Now we are looking at vacation options for this December, and I'm thinking that you'd lose at least two days of being able to truly enjoy the cruise because of the cold? Do they make up for this with indoor activities until we get to warmer weather?