While I can see the merits of using self-serve checkouts, I still don't think they're the panacea that everyone makes them out to be. It's only quick if people know what they're doing and are used to the process, but there are some customers who struggle with technology in general and end up taking so much time dealing with all the quirks and foibles that robotills bring. My dad became quite used to using them until he had his stroke, then it became quite painful to watch as he fumbled about with having to deal with his shopping, payment, Nectar card etc.; it would have been far quicker and, dare I say, kinder if the staff monitoring those tills had directed him to a staffed checkout. I was with my mum when she first used one of Asda's robotills and she vowed that she'd never use one again because it threw up so many errors and staff intervention was required several times.
If you have a large trolley full of shopping, or multiple trolleys, it makes zero sense to have the customer unload their shopping, scan it and then have to pack it at the end when having a member of staff in the middle can significantly reduce the amount of time it takes. Not everyone appreciates having help to pack their bags, but it used to be a "customer delight" moment when someone had loaded up with more than they anticipated buying and they were asked for help to pack their bags.
The whole scan-as-you-go thing isn't new (Shop'n'Go was a thing when I worked for Safeway years ago), and some customers might prefer it, but I really object to the removal of choice.