Most LED takes 12V input but if you are using 4S, 5S or 6S battery. Then you can use this to convert the voltage to 12V Output. Same story for 5.8Ghz Video Transmitter.
** If you use 12V BEC option, you must use a > 4S Li-Po battery input. A 12V Step Down Voltage BEC will only work properly if you at least 4S Li-Po. It does not make sense to use a 12V BEC if you use a 2-3S Li-Po battery. It is a Step Down Voltage BEC (NOT Step Up).