From the “you call this agile?” department by Joel Spolsky:

This is a simple article about basically choosing to sub optimize a part to optimize the whole. One of management’s roles is to determine when to trade a loss to one part of the system for the sake of the overall system. One of the big losses for software development is interruptions which distract developers.

The general consensus is that the loss from interrupting developers is much greater than for interrupting most other forms of work and therefor a great deal of effort is placed on improving the system to allow developers to focus. However, that should not prevent decisions that factor in that loss and conclude that taking that loss is worth the gain (to the rest of the system).

Related: Management Science for Software Engineering - Stretching Agile to fit CMMI Level 3 - post on Joel Spolsky’s ideas - Joel Management