One of the most important weapons in a programmers / coders / developers mental tool belt is the management of their “Psychological Flow”. Anything that disrupts this is bad for their productivity.
Paul Graham explains how the difference between Maker Schedules (coder) and Manager Schedules (PHB) do exactly this. The Manager Schedule is for bosses and is tailor-made for changing tasks, with each day neatly cut into one hour intervals, . Unfortunately, it spells disaster for people who make things, like programmers and writers, who generally prefer to use time in units of half a day at least. You can’t write or program well in units of an hour, says Graham, since that’s barely enough time to get started.
If you fall into the Maker camp, adds Graham, you better hope your boss is smart enough to recognize that you need long chunks of time to work in.
For those that don’t understand why interruptions can make programmers seem so brittle, an old post on Bruice Kroeze’s blog about Coding Flow and Techniques not only describes the problem but also suggests some ways that individuals can manage this.