Sofas basically define the living room. They are supposed to be the coziest thing in the living room so they must be as comfortable as possible.
While you need your beauty sleep, you also need a comfortable chair that you will need when having a serious talk with a partner, when you need a silent place to read a book and many more.
There are those hot days when you feel like undressing. Sitting at your balcony will relieve you of all that stress. They are a must have for a good view as well.
Preferably one chair is best for the kitchen.
A dining room is a must have in every home. While that is true, chairs and the table take the biggest portion. Table that rhymes with the chairs would be the best for the room.
The home office should preferably have a chair for work and a set of sofas around it. These chairs can be used for a brief meeting at home with workmates.