We begin this paper by asking a simple question: All beams can be simultaneously activated thanks to the ignorable inter-beam interference and sharp beam shape in mmWave networks This paper provides a counter-intuitive observation that interference between one-hop adjacent beams still significantly affects the network performance in mmWave networks. Leveraging this observation, we revisit an optimization of interbeam scheduling problem in a network-wide mmWave system on top of a physical layer precoding technique and suggest practical and low-complex beam on/off scheduling and corresponding user scheduling algorithms. Finally, via simulations in a real mmWave network environment, we reveal that the proposed algorithm attains close to the performance of an optimal policy which has much higher computational complexity.