As a client, using the self-checkout is (usually) a choice I get to make. I choose to use the self-checkout because it is often faster than waiting in a line. I am thankful for the opportunity to put in my own effort in exchange for faster completion and reduced prices.
I remember reading a study somewhere that the self-checkout isn't actually faster. It feels faster because you're busy instead of passively standing in line.
That depends on the implementation. E.g. Sam's Club lets you scan items as you put them into your cart and just walk past the registers.
In the local grocery store at rush hour, cashier lines are long and self-checkout tends to be quicker for buying 3 items. Taking a whole cart into self-checkout is slower than a cashier, because the self-checkout has like a 5% chance per item of going into "assistance needed" mode.
