Rooms are important for their inhabitants in various ways.
A living room is one of the most important rooms in a house because many people spend their time there, especially before or after dinner. It is also where guests stay when they come to visit.
The size and decoration of a living room will depend on the person who occupies it and on his desires. People with big houses can have smaller rooms than those who live in apartments or share homes with other families. Decorations are often personal preferences but adding pictures to your living room can make it even more interesting, as well as adding additional amenities like bookshelves or a fireplace that you might use to entertain yourself while watching TV shows.
Room is the most important part of a house. It defines what we live in. So it would make sense that room is the most important part of a house.