We have a living room, dining room and study, all much of a size. We spend most of our indoor time in the study. It is where many of our books are, our computers and a nice electric log burning stove, which gives a very cosy illusion in winter.
We have always had a study in every house we have lived in and what has always fascinated me is the number of tradesmen we have had in the house, who have really loved our various studies and said that their dream was to own a house with a room like our study, with books on the walls, a huge desk and a couple of comfortable chairs (and no tv).
As a child we referred to the main room as the sitting room. I lived in nearly 10 houses when I was young and in winter, when only one room was heated, which room that was varied. None had kitchens big enough so it was either the room leading off the kitchen or where the kitchen opened off the hall, the sitting room.