While the deployment of base stations (BSs) becomes increasingly dense in order to accommodate the growth in traffic demand, these BSs may be under-utilized during most hours except peak hours. Accordingly, the deactivation of these under-utilized BSs is regarded as the key to reducing network power consumption; however, the remaining active BSs should increase their transmit power in order to fill network coverage holes that result from BS switching off. This paper investigates the optimal balance between such beneficial and harmful effects of BS switching off in terms of minimizing the network power consumption, through comprehensively considering the spatial BS distribution, BS transmit power, BS power consumption behaviors, radio propagation environments, and frequency reuse. When BSs are deployed according to a homogeneous Poisson point process, the suboptimal and approximated design problems are formulated as geometric programming and the solutions lead to insightful design principles for the key design parameters including the spatial density, transmit power, and frequency reuse of remaining active BSs. The numerical results demonstrate that these solutions are very close to the optimal balances.