In the January 2015 HBR, Andrew O'Connell has a brief piece in the "Managing Yourself" column that talks about multitasking and the research that generally suggests it doesn't work as well as we like to think. The Pros and Cons of Doing One Thing at a Time - HBR
The idea that it’s better to finish your tasks in sequence than to jump around from one to another is very hard to accept, at least for me.
The negatives of multitasking have been reported over and over again. People struggle when they switch from one task to another to another without finishing. The tasks themselves take longer, and when those tasks are part of larger projects, those project suffer from loss of speed and flow (waiting for something to finish so the project can move to the next step).
But then the author looks for the loopholes in the "multitasking is bad" statement. He finds it in the idea that it helps keep the creative juices flowing and there are even examples of artists who find they do better when they have multiple pieces going (and out in the open in the studio, not buried on their computer). Of course, people need mental breaks from intense work. But these breaks are not moving from one intense activity to another equally-intense item.
The point behind these conversations is to help people see that things that block flow of work do much more damage than slowing down that one item. It slows down all their work. And it slows down the work of people who are dependent upon the results. If I were completely independent of others, then multitasking would only affect me. But I am not - my way of operating affects those around me. And visa versa.