The checkout wait is the time you spend in line at the checkout counter when there is no clerk to serve you (doing something else in the store) or when there are others in line ahead of you. Typically there is some space to put groceries on a counter or table (with a conveyor in modern shops) before one has to pay for them, which is the last opportunity to review one's purchases before paying. It is also a time to fish out coupons or frequent buyer cards, pick up impulse buy items specifically arrayed at the counter, and review the Consumerium buying signal one last time.
This, and the aisle walk past the retail shelf, are the only two sure opportunities to have the consumer review his or her choices. Typical timing of these walks and waits must be studied carefully to determine the performance criteria of Consumerium Services.