With no suspension, reduced tyre pressure can give a slight spring effect. This will reduce the effect of the unsprung weight of the bicycle bouncing around and occasionally lifting from the road. The rear wheel generally carries more weight than the front, so the effect is less pronounced and ideally you should run a slightly higher pressure in the rear. The softer front tyre will slow you down somewhat compared to a rock-hard one, but for commuting and general riding the other benefits may be worth it.