The caravan breakaway switch is like an insurance policy. You need it, but you hope you never have to use it. Here is a short explanation of how it works.
You have to make sure you check your breakaway switch before you leave on any trip.
The break away switch serves one purpose. It is attached to the switch, the other end to the tow car. If at any time the van becomes disconnected from the tow car, the pin will be pulled out of the switch and the brakes will be applied. 
So we need to make sure our supply battery is always connected and fully charged, we need to make sure the switch is operating. (The easiest way is to jack one wheel up off the ground, ENSURING THE VAN CAN NOT ROLL, release the handbrake and pull the pin. The wheel should no longer spin.
Hopefully this helps give you a better understanding of how the caravan breakaway system works