One approach to continuous improvement is to reduce WIP limits. When a Kanban System appears to be working smoothly, lowering a WIP
limit is analogous to lowering the waterline. It will expose the rocks, and new
bottlenecks and constraints will be discovered. As a result teams can work to
remove the new bottlenecks and constraints until work is flowing through the system smoothly again.
via methodsandtools.com, Aspects of Kanban by Karl Scotland