Open an old plan drawn on the Vāstu Puruṣa Maṇḍala and you will find the middle of the grid marked, but unbuilt. This is the Brahmasthan, the centre, and the instruction is consistent across the texts: keep it light, keep it open, do not load it.
Why the centre matters
Practically, the centre of a building is its lungs. In a courtyard house it is literally open to the sky, pulling warm air up and drawing cooler air through the rooms around it. Cross-ventilation organises itself around a clear middle.
Put a heavy, sealed function there (a toilet, a store, a staircase core, a lift shaft) and the house loses its breath. Air stops moving through the plan and starts pooling in the corners instead.
The centre is not wasted space. It is the space that lets every other room work.
Reading it in a modern flat
Few homes today have a courtyard. But the principle still reads: the geometric centre of your plan wants to be circulation, light and air, not a locked, airless box. When we analyse a home, finding that exact centre is the first thing we do, because everything else is measured from it.