Despite my frequent rants about self-checkouts, there is one good reason to have them.
If you only have one or two things, you don’t want to wait behind an enormous weekly shop. A self-checkout or basket-only lane is a good solution here.
Similarly, its a good idea to split the bakery queue into ‘sandwiches’ and ‘bread’, so bread buyers aren’t waiting behind the office lunch order.
Sorting a big queue into separate, differently handled sub-queues reduces queueing overall, and makes handling the different types of order easier, because you’re not switching between them all the time.
Better for everyone then.
Forcing everyone into the self-checkout queue defeats the object though.