At least where I am in the southern US self-checkout ends up being slower.

Ten years ago my experience was likely similar to yours, pretty quick to just scan your own groceries, not much of a line to speak of as some people are opting for a cashier. Go for the self checkout every time.

The trouble now is that there aren't enough cashiers so almost everyone has to go through self checkout. Longer line but you would think it wouldn't make that much of a difference.

But they only have one attendant watching all the self checkouts. So if three people are buying beer at once you have only one to go around checking their IDs. If an item (usually a fruit or vegetable) doesn't have a proper entry in the kiosk's database and no barcode to scan then the attendant has to go by and manually enter a code scan the item to unlock the machine. For example when buying habaneros my grocery store only had an entry for "green habaneros", if you selected them the machine would call a cashier over because you picked an item they don't actually have. Don't even get me started on their touchy anti theft measures erroneously triggering because you moved your hand weird when setting down a bag.

Again, none of this was really a problem back then, but now at my grocery store it's one attendant handling 8 self checkouts at once where any number could have these problems to resolve.

This part may be more in my head, but I also frequently feel like I'm stuck behind people who have never used a touchscreen before, or been in a grocery store, or exchanged currency for goods. Someone always needs help with some part of the process and if you add that to the problems I listed above, it can really slow things down.