the garbhagriha concept you mentioned was a product of Adi Shankaracharya as you would see the entire temple architecture built by Shankaracharya is based on the energy principles including the stambha outside the sanctom plated either with gold or silver and has a copper lining or wiring that goes right to the earth. To maintain the energy levels intact in atleast these temples, they avoid devotees from entering into the garbhagriha and is allowed to only the priests post they follow a certain regime to gain the energy levels themselves through pranayama and other Vedic processes.

The point I am coming to is that the concept of prana prathistha is to treat the idol like a living being who wakes up, cleanses himself, dresses up, eats food, sleeps in the afternoon, goes for a stroll etc. the cycle continues.

The cleansing of body, mind through meditation and soul through reflection is the very essence of the practise.