Currently, two cooperative transmission strategies, Coordinated Multi-Point (CoMP) Transmission and wireless relaying, are expected to be deployed in future cellular systems to improve the performance of cell-edge users. Due to the cooperation diversity, these technologies can potentially lead to more energy saving. Therefore in this paper, we analyze their energy saving performance with an average outage constraint. The impact of the traffic intensity and BS density are also investigated. Based on the typical parameters setting, our calculation results show that traffic intensity can be divided into three classes: "coverage-limited" region, "energy-efficient" region, and "capacity-limited" region. The coverage-limited region prefers offline fixed algorithms, while dynamic online algorithms are more suitable for the energy-efficient region. As BS density goes higher, the energy-efficient region becomes larger. However, the traffic load region where the coo...