Why all those layers of little springs in a John Lewis mattress?

Hi
I am interested in your Artisan range. I have looked at the John Lewis range in store and am told about the many layers of tiny springs on top and below the main pocket springs. They also say that their pocket springs have two springs inside each case. It is confusing. Can you tell me why they have done this and if there is any benefit, before I buy an Artisan Luxury mattress please?

Thank you.