>If you don't have any alcohol you can use it without interacting with anyone at all and its much faster.
I agree that you can do it without interacting with anyone at all. But I question whether it's faster.
For a class assignment on usability a while back, I observed self-checkout users and manned ("proper") checkout at a local grocery store and found that the absolute fastest of the self-checkout users were only just as fast (per item) as the average manned checkout user (among 24 users).
A few factors increase the speed of manned transactions. First, cashiers are familiar with common
produce numbers, avoiding the need to search for stickers or slowly look up the number of a particular
item. Second, a cashier can begin bagging items as the user pays by credit card or pulls out cash, so
some of the work is done in parallel. Third, sometimes manned checkouts have a person dedicated to
bagging, which reduces the time even further (though all times recorded for this project are single
cashiers without baggers).
Self-checkouts definitely feel nicer for me (except when the anti-theft "place item in bagging area" nagging starts). But now, when I'm in a hurry, I'll make a beeline for a register with a cashier instead of the self-checkout.