It is thus more appropriate for resource-demanding tasks like audio/video streaming or network routing than low-power sensor application like the ones targeted by the ESP8266 chip.
However, the AR9331 features the lowest power consumption for this class of SoC, with only 0.5W @ 18dBm Wi-Fi. It is possible to throttle the power consumption down, but you will never reach the 78µA of the ESP8266.