Some machines use scales to measure the weight of items, scan one item, put it in the "bagging area" (scale), repeat. Many stores have disabled scales because they're buggy and don't catch thieves, who learn that to steal, don't put items on the scale. Now, stores have employees watch and offer "technical support". "Oh, ma'am, I think this item may have been missed. Let's check. Do you need help with how to scan items?" I don't try to steal, so don't find the machines to be a problem.