Ranger: The switch, just like the insulated pins are ad hoc solutions. Originally, plugs were simple and "dangerous", like the US 15 plug. Different solutions were worked out in different countries. These include:
1.) Improved plug grip to prevent the hand from slipping.
2.) Switching
3.) Insulated pins
4.) Recessed sockets
The switch offers the additional benefit of eliminating the arcing when you insert or remove a plug under load. For this reason the large (63A and 125A) IEC 309 plugs have a pilot pin that switches the socket off when there plug is removed. A similar result could have been achieved by using insulated tips on live pins.
