Duty cycling has been widely used in Wireless Sensor Networks (WSNs). While its general impact on the network performance is intuitive and clear, this understanding is far from sufficient for WSN planning, design and optimization, among others. In this paper, a quantitative study on the relationship between duty cycle and end-to-end network performance, in terms of delay and throughput, is presented, where the network diameter is also taken into consideration. Particularly, closed-form expressions are derived, revealing the impact of duty cycle on the end-to-end performance in a wireless sensor network. Numerical results illustrating the impact are presented and discussed.