How does absence of any resistance in a circuit or a conducter means no power loss at at all?

When there is no resistance in the conduction of electricity, you have a super conductor. All materials have resistance to the flow of electrons, and certain materials, when super-cooled can reach super conductivity, they allow the electricity to flow without losing any power. Applications of future super conductors which will operate at warmer temps, include power transmission and levitation, like on a Mag-Lev train.