Coffee Cup Kanban
Coffee bars employ a couple of different strategies for taking and filling orders. Each strategy makes different tradeoffs.
Sometimes someone will take your order, ring you up, and then make your drink and give it to you. Other times someone will take your order, mark up a cup with the details of your order, place the cup in a queue to be picked up by a barista who will make the drink and then place it on a shelf and call it out.
That second arrangement is a kanban system, and the cup is the kanban. The cup-ban doubles as an order form that can encode most combinations that a barista should expect.
There are reasons to choose one process over another. Small or lower-volume shops with only one employee on shift usually apply the first method. Larger, higher-volume stores with two or more workers on shift usually apply the second method. The store using the kanban method gains the advantage of taking your order (and collecting your money) quickly. [...]
It is good news for you when the barista asks you, "can I get a drink started for you?" because that should mean he has slack capacity. [...] [O]nce the kanban queue starts backing up, the cashier should start stalling, even if that appears to make the cashier queue back up. The second queue has limited capacity before waiting customers start crowding each other or irritating seated customers.
Some shops get obnoxiously long lines during the morning rush. The solution to that often appears to be adding an additional espresso machine, because the making of the drink ends up being the bottleneck.
The trade-off for businesses is that the rushes don't last, and then the surplus capacity goes unutilized for most of the day.
-- Corey Ladas
from "Scrumban: Essays on Kanban Systems for Lean Software Development"
Quoted on Sun Jul 22nd, 2012