It is known that the Rutherford engines run on an electric pump-fed cycle. There must be a trade-off between the tank pressure of the electron rocket and battery capacity, for batteries are dead weight on board. To reduce the amount of battery dead-weight the tank can be at a slightly higher pressure. Too much tank pressure, and the structural weight increases.
So an optimal pressure for the propellant tank can help a lot and this might be higher than the usual pressure at which the propellants are stored in conventional rockets.
What is the tank pressure of Electron rocket?