The potential difference between two points in a good conductor can normally be neglected because the loss in the line is tiny relative to the power transmitted or used by the source/load devices.
The ability of a conductor to carry electrical power over long distances is important in the construction and operation of transmission lines. In order to overcome power loss over long lines, alternating current is used with high voltage in thick steel strengthened aluminum wires. The power lost in the line is tiny when compared to the power the lines are carrying.
After the power reaches a building or group of houses, the high voltage is reduced to useable power for appliances we can all use. Now the wiring is much shorter, and the appliances will be consuming much more power when measured against any voltage dropped in the cord connecting it.
Even looking into your cell phone or computer, the thin wiring inside is still capable of carrying power to the integrated circuits from the battery. But the power lost in the wiring is negligible compared to that supplied by the battery and used by the device.