My preference is to use Scan and Shop, so I’ve already packed straight into my bags and all I have to do at the end is pay. Second choice is to self-scan at the till. I avoid using manned checkouts 1) because it’s dreadfully time-wasting to handle my shopping three times in store - to load the trolley, unload onto the belt, then load into bags, and 2) I don’t want my food handled more than necessary.
I’ve recently retired from part-time on checkouts at Waitrose, which I thoroughly enjoyed, but SO many people could be in and out very much faster if they scanned their own shopping.
It’s a silly misconception that you’re “saving someone’s job”. All shop floor staff, from 16 year olds to 80+, receive till-training as part of their first week’s induction. Some enjoy it, and if accurate and careful they might prefer to always be on a checkout. Some dislike it and prefer to be in the warehouse or replenishing stock on the shelves. Only the fresh food counters, welcome desk and café are options for more specialised training. Every cashier released from a checkout during quiet enough periods, when self-service tills are being well-used, will be filling shelves so all the customers get a better experience, and will be called to open another checkout if queues start to build. Same number of staff, better deployed, they don’t lose their jobs because self-service tills are there!