Free labor - not with the portable scanner type of self-checkout. You put stuff directly in your bag instead of the cart, so no extra effort is necessary. Although tbh, even the scale-type machines are quicker to use than waiting in line. They do perform randomized checks, but very rarely and only 3 items ie 1-2 minutes total delay.

Plus with contactless payment my shopping is an essentially frictionless walk through the store building.