Quite handy for largish buildings. Run a 4/6mm from the CU to where the ring is needed. Great for confusing the youngsters.
I think we used 6mm when we got around to rewiring the brothers 4 floor + basement house. Both of us electricians, it only took three years to finish.
We used to do this in labs for bench sockets when I was an apprentice. 6mm to a 30A switch above the bench, from there a ring of sockets for the bench.