This is because local power for devices, including rail capacitors, have an insane maximum power draw rate, and if there is power in the ship, they fill it. For this reason, there is really no point using the capacitors on anything that is not mission critical, because its just a dedicated battery to that device, that can't be drained by other parts.
So, yes, there is! And yes, its pointless, because we can't control device power priorities so using these internal power containers only helps when the ship is empty.