Some power supplies cannot ramp up to the full 5V that the Beagles requires fast enough for the Beagles to recognize the change, particularly if there is significant load (lots of pixels) or capacitance connected to the power supply. In those cases, the Beagle will not boot. A time delay relay can be used to delay the application of 5V to the controller until a few seconds after power up so the power supply has time to get to a full 5V. Most users will not need this, but some do. Users using 12V will also not need this as the onboard buck’s will ramp up fast enough.