Along with poor processing and storage capacity, each sensor in wireless sensor network (WSN) is equipped with a limited energy resource and difficult to be replaced in most application environments. However, the designs for wireless sensor networks focus on not only energy-efficiency issues but also other problems such as fault tolerance, scalability, latency, and network topology. In this paper, we mainly focus on balancing latency and energy-efficiency as primary design objectives of routing protocols for WSNs. Our presentation is accompanied by analysis of the current state-of-the-art of routing techniques for optimizing energy-efficiency interested in latency factor. Furthermore, we propose a new research direction to balance energy-efficiency and latency in WSNs.