Please someone explain the headlight relay mod

[VWBeamer]

You just need a 4 blade relay. The five blade relay has power on the fifth leg when power to the relay is off.

The lights are brighter because your are eliminating all the resistance of the stock light switch and associated wiring.

It also makes your stock light switch last longer, because the current it's conducting is a lot less. This benefit may be subjective, but non the less is a benefit.