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Multitasking

It has also been well documented that multitasking leads to a reduction in production rate [Clark 1992]. If a schedule is estimated using an aggregate technique based on average times for Features of a particular complexity, that metric does not take into account any downtime caused by multitasking.

Switching from one task to another incurs a Setup time and a reimmersion time for the developer. This will reduce the production rate and increase the Feature Lead Time. The effect will be to eat away any buffer in the schedule because the level of effort estimate against incurred Lead Times will be out of sync.

If the developer as a capacity constrained resou...

From

Cover of Agile Management for Software Engineering: Applying the Theory of Constraints for Business Results

Note

working on more than one project.. :-)