The regulator’s enable input, EN, is pulled high (to 5 V) internally, which enables the regulator by default. The EN pin can be driven low (under 1 V) to disable the output and put the board into a low-power state. The quiescent current draw in this sleep mode is dominated by the current in an internal pull-up resistor and the reverse-voltage protection circuit, which altogether will draw between 5 µA and 10 µA per volt on VIN when EN is held low. To bring the board out of this low-power state, the EN pin should be pulled above 2 V. If you do not need this feature, you can leave the EN pin disconnected.