When the kid were very small, we used the second floor library as a family room, because the sunroom downstairs was freezing cold most of the year. Over time, however, the library became the catch-all space: piles and piles of books and papers, and no where to sit.
Transformation! We still need to purge the bookshelves, and that "Large Box" is sort of like a kitchen junk drawer at the moment. But the new chairs and ottomans are wonderful!