I read about this, and did this once.
It is a way to fluff up a garden that has become too compacted.
It is a LOT of work:
Dig a trench 12 inches deep, 12 inches wide, the length, either way, of garden and transport that dirt to the other side of the garden on the edge. Now move over apprx. 24 inches and dig another 12 incb trench putting that dirt into the first trench.
Do this the entire length of the garden and then move back the other direction doing the spaces missed by digging every 24 inches.
It raises the garden, my dad was amazed it worked, and brings newer soil to the surface.
Bob