According to Donald Reinertsen, the key to improving flow in product development is to manage queues.

Queues are the biggest source of waste in product development processes, but they are invisible, unlike in product manufacturing, where queues and inventory can be clearly spotted. In software development, queues and inventory are invisible.

What are the problems with queues?

  • Queues increase cycle time. By quantifying the cost of delay, we can attach a specific financial cost to queueing time.

  • Queues increase the risk of a product development process. The longer the transit takes, the more vulnerable we are to changes in customer preferences, competitor introductions, and shifts in the underlying technology.

  • Overhead: The more projects there are in progress, the more projects there will be to track and report on. Even worse, for more progress reports per project will be demanded because queues lead to long transit times.

  • Queues reduce quality by delaying feedback from downstream processes.

  • Queues have a negative psychological effect. When the next process requires to be finished within an hour, there is a sense of urgency. When the next process has a 4-week queue, employees may feel little value in hurrying to finish their work. This usually turns into an organization-wide vicious loop of getting slower and slower.

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