The self-checkout lane is a good idea in theory. People with only a few items can scan them, pay, and be on their way. But in actuality you have to catch them at the right times.
These lanes were designed for customers to scan 1-15 items, pay, and leave. They aren't as quick to scan as the scanners the cashiers have. So when somebody walks up with two shopping carts full of groceries it defeats the entire point.
The other problem plaguing these lanes is senior citizens. They walk up to the aisle with a smug smile on their face and scan one item every 3 minutes, needing the cashier's help for every other item. I can't tell if they're smiling because they wrongly think they're being independent and doing something for themselves or if they just enjoy wasting everybody's time.
Earlier today some older woman had tried to scan a two-liter of soda and put it in her bag. The item didn't scan and the machine told her to rescan it. She ran it over the scanner again, and again didn't even point the bar code at it and she tried to put it in her bag. Eventually she got frustrated and walked away. I'm not sure whether she walked out without paying or went to a regular checkout lane, but either way she was wasting my time.
If you're too dumb or incompetent to use modern technology then perhaps you should leave it to the younger generation who know how to hook up a DVD player without calling an electrician.