The dipswitches are mainly there to let people know their board is working during initial testing or desktop deployments. Anytime a board is deployed in the field as a “sleeping” station, power savings are important during the sleep period. So I put the dipswitches on the new versions of the Mayfly to allow people to deactivated the LEDs. The dipswitch for the green LED only cuts power to the green LED and nothing else, but it will save you about 2 mA. The orange LED is only on if power is being supplied through the USB jack, like when connected to a computer or when powering from the USB jack like what that converter will do. Whenever the USB jack is powered and the USB dipswitch is on, the LED is on plus the USB converter chip, which draws some not-insignificant power, so turning off the USB dipswitch will save power and prevent the USB converter from being on constantly. However, you’ll just have to remember to turn that dipswitch on again in the future if you ever decide to reprogram that Mayfly or want to connect to the Serial Monitor to see some output.
There’s a description of the dipswitches and all the new circuitry on the Mayfly Hardware Details page.