Flow Efficiency
The proportion of total elapsed time in which work is actively being progressed rather than waiting, typically far lower than anyone expects.
Active time divided by total elapsed time. For most organisations the answer is between 5% and 15%, which is the single most useful number a value stream exercise produces.
The consequence is direct: optimising the active work has almost no effect on delivery speed. Making a two-day task take one day changes a forty-day lead time by 2.5%. Removing a two-week wait changes it by 35%.
Yet almost all improvement effort goes into the active portion, because that is where the visible work is.
Where the waiting actually sits: approval and review queues, handoffs between teams, waiting for an environment or a shared resource, waiting for a dependency from another team, and batching, where work waits for a release window.
The remedies follow from the location rather than from general efficiency: reduce handoffs by giving teams end-to-end ownership; replace approval gates with automated policy; remove shared-environment contention; and reduce batch size, which is the most reliable single lever because it shortens every queue simultaneously.
The organisational point: flow efficiency is a property of the system, not of the people in it. A team working flat out inside a 10% flow efficiency system cannot fix delivery speed by working harder, and telling them to is the standard mistake.