Reduced power usage is the main reason for building custom boards with ESP8266 since most of the modules such as Wemos and NodeMCU use power regulators and UART to USB chips that draw a lot more current than the 20μA required by the ESP8266 during the deep sleep. In my own testing with Wemos D1 mini v3.0.0 the power consumption during the deep sleep was around 18mW because of all the extra components.
TrigBoard by Kevin Darrah is a great example of reducing the power requirements to an extreme.