I use a PBD in a lot of my stuff, I really like using them. Great for add ons like FPV, almost a necessity when doing FPV with a sophisticated auto pilot. In the case of that particular pack, IIRC, the escs dont have a BEC on them so you need the 5V output on the board to run the receiver and the servos. There is also a switchable 5v for camera gear and a 12v for things like transmitters. I think it's all written on the board in a pretty easy to see manner.