It depends on the store. There are places where the self checkout lanes are dysfunctional and end up requiring waiting for a checkout worker (who are usually understaffed) to come and scan a code to fix it.
My local king soopers always allowed a super low volume setting if you clicked it, now there's only two, yelling and screaming. People were probably setting that and the beep couldn't be heard on the camera or something
European here. Our self-checkouts make no sounds and don't have any of that unexpected item bs. The experience is great. If your experience is like what I've read here, I begin to understand why it's disliked.
Not always though. But regardless if you agree there, they are slowly replacing humans with machines and that has negative implications for workers and for the economy
It's not faster, but it can be easier if you really don't want to talk to people. Don't kid yourself: someone who spends hours per day scanning barcodes knows where they are on each product and can do them faster than you.