Will depend on the type of shop, local, and local demographics.
In our village Co Op, virtually everyone uses the self service machines.
The shop assistants only go to the "proper" till/counter if someone's waiting there, otherwise they're all busy on the shop floor, filling shelves, tidying, helping with customer queries, etc.
From casual observation, I'd say most customers only go to the counter to buy cigarettes, lottery tickets, etc.
And this is a village with quite a significant elderly population, most of whom seem to be able to use the self service tills well enough. Though, must admit, the staff are VERY helpful and happy to spend time showing people how to use them.