I agree with fff.
I suspect that the savings and utility will come with new construction where, for instance, the load carrying copper wires only go to the outlets or lights and the controls, which could control the light, socket, etc. could be wireless but their power would come a separate low voltage, low amperage, circuit this saving quite a bit of copper. The smartphone could control selected or all circuits but would not be the only control.
As an example thermostats control furnaces and air conditioners via low voltage, low amp, wires. New ones may also be controlled by a smartphone or computer.
It's probably not very cost efficient to convert existing homes in most cases.
BTW I get points when I mention that I can't go out as I need to update the firmware in my front door lock.