I always use self scan and have done for years. That way, I can scan and pack my items in the order I want to according to shape, size and delicateness and at the speed I want to rather have them coming at me fast down a conveyor belt, piling up in a heap at the end.
I can also check prices as I scan, which you can’t do if you are having to hurry to pack as someone else scans, plus I can treat fruit that bruises more gently.
With self-service there will usually be multiple tills open so, unlike staffed tills, you don’t feel rushed or guilty holding up the person behind you who chose that queue to join. I’m no slouch but I like to do things at my own pace and not at a pace dictated by someone else.
The saving jobs argument is a non-starter as supermarket staff are often rotated to a multitude of jobs e.g. shelf replenishment, pick and pack for online shoppers, bakeries and deli counters, customer service tills, sales of tobacco and lottery tickets or back room jobs we never see like dealing with stock as it arrives. I don’t imagine there is a ever a shortage of job to do in a busy store.