Daniel J. Levitin on the benefits of monotasking and daydreaming, for The New York Times: 

If you want to be more productive and creative, and to have more energy, the science dictates that you should partition your day into project periods. Your social networking should be done during a designated time, not as constant interruptions to your day.

Email, too, should be done at designated times. An email that you know is sitting there, unread, may sap attentional resources as your brain keeps thinking about it, distracting you from what you’re doing. What might be in it? Who’s it from? Is it good news or bad news? It’s better to leave your email program off than to hear that constant ping and know that you’re ignoring messages.