Previously, many researchers sought to optimize the throughput and power consumption by radio transmission power control, but the experimental platforms and the workloads did not reflect the reality of WSNs. We present a dynamic transmission-power-control algorithm based on previous studies and evaluate the algorithm using realistic multi-hop WSN workloads and a large Mica2dot-based testbed. We have found that potential gains of dynamic transmission-power control are much smaller than what is indicated by prior research. Compared to the fixed transmission-power control, the dynamic transmission-power control improves the power consumption up to 16% for convergence traffic, but no noticeable performance improvements for aggregation traffic. The effect of dynamic transmission-power control becomes larger as we reduce the radio duty cycle, with 37% power savings at a 10% duty cycle. This result suggests that dynamic transmission-power control is most useful in combination of low-power MAC protocols which implement radio low duty cycling.