According to the Kanban Guide for Scrum Teams, Work in Progress (WIP) limits are set to control the amount of work in progress in a system, enhancing flow, reducing bottlenecks, and ensuring smoother delivery. WIP limits can be changed as a result of an inspection and adaptation cycle, which primarily occurs during the Sprint Retrospective.
During the Sprint Retrospective, the Scrum Team reflects on its process, practices, and interactions. This is the time when the team inspects its flow, evaluates the effectiveness of the current WIP limits, and can make decisions to adjust them based on observed issues or potential improvements. The goal is to optimize the team's ability to deliver value, and adjusting WIP limits during the Retrospective allows for thoughtful consideration based on the team's experience and data from the completed Sprint.
Changing WIP limits at other times could disrupt the flow and reduce the predictability and stability that the limits are intended to create. Therefore, the best practice is to evaluate and change them during the Sprint Retrospective, where the team can inspect the results of their workflow and make informed decisions for the upcoming Sprints