Exactly, typically living rooms, bedrooms, children's rooms, studies, guest rooms receive a supply air valve. Fresh air is blown into these rooms. Bathrooms, guest toilets, kitchens, utility/storage rooms receive exhaust air valves in return, where used air is extracted. Hallways/staircases typically do not have valves. This means that the fresh air must flow from one room through the hallway to the other room with the exhaust valve. There are different options for this overflow, some with and some without sound insulation. Through the door or also through the wall (overflow valve).
If overflowing is not possible or not desired, each room needs supply and exhaust air. This means a higher effort in construction. In addition, the airflow in the room must be considered (avoid short circuits), which may be more difficult than with overflowing. One should then consider a decentralized system, where overflowing can also be omitted.