I don't use DIY checkouts at all, even if I've only got one item I'm getting in line and the person behind the counter gets to make small talk with me.
I don't agree with DIY checkouts, its not like the price of the items will come down when staff lose jobs.
Plus it removes some younger kids from earning some $$$ to get their first cars.
It might not be many staff but surely you would be down a few?
Imagine you coming to me and explaining your car has an electrical problem, and then I tell you how to fix it and you pay me and do the work yourself.
Maybe its a training scheme, by the time you hire the pimply faced 14 year old kid, they've already done 5 years of DIY checkouts by shopping with their parents and know how to do it efficiently