Deano ... consider the old method in domestic premises , back in the 1940s - 1950s , rubber cable , sockets could have been a mixture of 2A x 2 pin .... 5A x 2 pin ...5A x 3 pin .... 15A x 3 pin or use a bayonet adaptor, remove the light bulb and plug into the ceiling rose.
The 15A sockets would all be wired back separately .
So back then , one simple ring main using 13A BS 1363 sockets would be adequate for a small house .
It saved cable .
It could be added to.
It standardised all the plug tops .
Not uncommon to find a 4 way board for a house :-
8 Lights
6 Plugs
Cooker
Imm. Htr.
You need to know that the names of things in this trade are like the staircases at Hogwarts , they keep being changed by those above us and the use of initials is encouraged until idiots like me don't know what others are talking about .
To understand types of Supply you need to speak latin and it all makes sense ..so for Earth say Terra , as in Terra Firma then a TN-C-S begins to make sense.
Spur units are now FCKU or something .
Fuseboards or "The Board" are CUs or a Consumer's unit shortened to Consumer Unit.
The obvious one of course was to change all the cable colours .
Fuses are now OPD s or something similar , so it goes on .
Conduit & trunking is now Cable Management . And so it goes on.