The only self checkout machines I've ever seen that actually seem to save time are the ones in IKEA. That's only because people are buying such bulky heavy items that they don't bother weighing them. It's the scales that cause all the problems, they are sensitive enough that they can detect if you put so much as a single piece of paper on them but are I'll let down by the fact no one weighs the original product.

Oh there's an unexpected item in the bagging area is their, could it possibly be that loaf of bread I just scanned? No apparently not because this product is overweight by a whole nanogram.