The unevenness or mura of the work wreak havoc on our work. Project demands fluctuate and working on multiple projects likewise creates or exacerbates the unevenness. In product development work can get heavy around gate reviews as the project must accomplish certain expectations and milestones are reviewed in the gate activities. One functional department may not be at capacity, but anther may be running beyond capacity. The arrival of the work from one department stacks up as input to the next department. This then creates muda as we have waste in the form of over production. All of this unevenness has impact on schedule and the people performing the work, and sometimes specialized equipment as the demand fluctuates wildly.
Material that our development team will use may also be subjected to this unevenness, think prototype parts, upon which we will test and learn about the product for the next iteration of the development loop. When lead times are long, we may purchase these prototype parts in quantities larger than needed creating an unevenness of available parts that then become waste.
External events such as accepting projects that push our product development and manufacturing system to the brink in terms of capacity and also have times when our system and staff are not very busy at all are examples of unevenness.
We can reduce this unevenness through the use of a kanban system or a pull system for the work rather than an arbitrary schedule driven system like Gantt charts.