Bill Wright presented the following explanation :
Harry Bloomfield wrote:

I've never understood why this 'alternative' method isn't more popular.
The Wikipedia article says it "can cause confusion" but, come on, it's
only wires and switches - you don't need a PhD to understand it!

In my experience people with a PhD are no more likely to understand
electrical installation than anyone else.

Bill

Those words you quoted were not written by me, they were written by
Richard Russell.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk