Since I shop almost exclusively at Aldi in my town, I bag all my own groceries but the cashier scans them. Part of the reason they are so good is that they are treated well (they get to sit, for instance--I think it's ludicrous that cashiers have to stand all day, there's no good reason for it), part of it is they're well-trained, and part of it is they're not arguing with or waiting for baggers. If the cashiers in other stores were as good, fast, and friendly (as opposed to overly friendly and nosy) as the ones at Aldi, I'd probably 1) go to the other stores and 2) utilize the cashiers. As it is, I *always* use self-checkouts in my town if I have to go somewhere besides Aldi, and they work better for me than the cashiers. If I go through a cashier line it takes me 10-20 minutes, minimum, at any of our local stores (I wish I were exagerating). It's the same at our local bank, so I also never go in and use a teller (I've literally never once gotten out of our bank in under 20 minutes, no matter how few people there were waiting). Since I am only ever there to buy one or two emergency items, I am just not willing to stand in line through the endless chatter, mistakes, slowness, and nosiness of our local cashiers.
It also allows me to bag my own groceries in my own bags. Ecologically, this is great, and our local stores all but refuse to do it. I've actually gotten rude comments from both cashiers and baggers when bringing in my reusables! It's also great to bag my own groceries because I am often buying for clients. Smooshed bread would not go over well.
When I shop at Wegman's, which is unfortunately 45 minutes away, I always go to a cashier. One of the reasons we go to Wegman's is that they manage to offer cashiers and friendly, fast service at lower prices than our local (also chain stores) grocers. There are many other reasons (such as the produce isn't moldy at Wegman's, while it is at both our local Safeway and Food Lion most the time); but, I find it interesting that Wegman's can offer great service and equal or better products at lower prices.
If the service was better in stores, I'd likely do regular checkout instead of self-scan; but, as it stands, I'll keep using the self-scan and bagging my own.
"This isn't life in the fast lane, it's life in oncomming traffic." -Terry Pratchett