I use self checkout only at places I don't have coupons and have only 1-2 items, but I hate them with a passion.
The scanners are terrible at certain labels, especially bulk meat which they have to go get a gun to scan the barcode or enter it manually.
They are terrible at accepting gift cards and coupons.
So many stores have stuff mispriced that its just going to be an argument anyway so why not just stand in line and let people use self checkout that don't care what they pay.
The typical problem is that they will mark one product as sale or related to a coupon but not ALL the products it applied to and since that all seems to be keyed in manually at grocery stores, its high probability of failure.