Tyre pressures are derived from the axle weight and contact patch area.
Under inflation will allow the tyre to flex excessively and potentially over heat.
Over inflation is less concerning, some police pursuit drivers will inflate their tyres to the max permissable to give pin sharp handling, at the expense of ride and a reduced contact patch area.
Generally, for normal day to day driving, it is always better to stick with the manufacturer recommended pressures and especially any front rear delta.
The pressures are recommended for a reason, not simply plucked from the air....