I can understand you: beyond a certain size, I ask myself the same question. However, only if rooms are duplicated or a guest room is planned, even though you only have overnight guests twice a year.
that then feels like a dance hall
When you furnish the room, certainly not. You don’t just place furniture against the wall, but zone different areas. The reading chair can easily take up 8 sqm, and you don’t see it.
you especially have to keep all that clean
... And around the reading chair, vacuuming/mopping is easier to do than if it stands on 2 sqm and you have to move it aside to get behind with the mop.
That you usually don’t need the space is another matter. The golden mean or to each his own, everyone is allowed that as long as they don’t spoil the 120 sqm hard-earned square meters for others.