The why
In Dome A, I have residences and factories, so I have no penalty. Colonists go to Dome B for services.
In Dome B, I have a lot of residences and services. I accept all colonists, especially Saints, empaths and children. Thus, when the child finishes school and becomes a teenager, he automatically earns several bonuses since his house is B.
If I put the nurseries in the dome C, the children, become teenagers, will move in a random dome and will not receive any bonuses if they do not go in B.
Traveling the saints or teenagers from one dome to another is more than tedious. My method automates everything very easily.