To me it’s a middle to upper class thing, in our house we didn’t even have our own room each let alone another space for sofasI hate the concept of snugs. For most peopling seems to mean that they’ve squeezed a sofa into a tiny corner of another room and grandly named it a snug.
not a proper snug which is another room that is maybe smaller than your main lounge and so given a cosier vibe maybe with a fire and throws and cushions, painted a darker colour to enhance the cosy vibes. Not a corridor to the utility room.