WIP limit can have profound effect on our Lean management thinking.
A good guess is to set WIP limit as 50% more than the current number of people working in the stage. Setting WIP limit to higher figure can lead to overwhelming the resources and create clog in the way of the flow. Setting WIP limit, at less than the head count, is undesirable in-general since it means having un-utilized people.
Though WIP limit can be changed once it has been set, I suggest that it should be under change control. For example:
– WIP limit should be revised monthly or after every release.
– WIP limit should be changed when significant project event occurs.
If we are derived by the Theory of Constraints, then, WIP limit can become a key tuner to promote the flow of value in the system.
If a stage can’t accept a new work due to reaching WIP limit, then, this work gets queued. Rather than blocking the work, this mechanism regulates it. The work would not be done any way if we allow it to enter the stage; instead it can slow the overall speed of the stage leading to more delays.
If the coming work item is urgent, then the stage can allow exceeding its WIP limit to allow processing this work. It can mean putting some in-process work on-hold. If the number of urgent work items exceeds 5% for the overall system capacity, then, the system should be reviewed.
I experienced first-hand how developers who under-value the WIP limit can create stage with many unfinished work items. The overall flow is reduced to the speed of this stage.
Allowing more than the WIP limit from my view is insanity. For me this is attitude coming from certain developers. The analysis of those developers almost showed me that they are single point of failure at their department or team. The root cause is management issue which while allowed the abundance in certain skills; management didn’t pay attention to the knacks known by one person.
Respecting the WIP limit leads to confrontation and sometimes resistance from these unique skills. WIP limit serves to have the risks materialized quickly. To succeed we should proactively address the root causes. This is at the heart of change management!
How an organization can be shifted from being dependent on hand-full of heroes so that it can provide sustainable delivery across teams?