The right tyre pressure guarantees low rolling resistance and also better response between the torque sensor and the motor, and has a significant impact on preventing punctures.
Depending on your body weight and desire for comfort, you can vary somewhat, but too low tyre pressure can cause the motor assistance to stop or the ride to feel much more sluggish - and the risk of punctures due to so-called "snakebites" is considerably increased.
In general, the indication on the sidewall of the tyre is the maximum value, and you can still go down a little with the tyre pressure, but never beyond.
The graph below shows a suggestion between comfort and speed. You should check the tyre pressure before every ride or at least once a week. We recommend buying a floor pump with a pressure gauge which clearly shows the tyre pressure.