There are lots of ideas out there on productivity and multitasking. Many take a black-or-white view; it is either a good thing or a bad thing.
My take is that you have to understand what multitasking means. Just like a computer, multitasking gives the illusion of doing more than one thing at a time by quickly context-switching between tasks. The catch, is that in a human mind, context-switching causes significant lag. This lag is referred to by terms such as “losing focus”, “getting distracted”, “wandering”, or even “procrastinating”. However, a lot of multi-taskers may not even know that they are suffering from this problem.
Context-switching costs productivity in cases where you need significant focus. Basically things that involve high-level brain activity like creating or problem solving. You know, the stuff that matters. Multitasking in this area is a terrible idea. It leads to a common syndrome – instead of doing one thing well, you attempt lots of things, and get nothing done. Then, when you stop and reflect, you are left wondering where your day went. This is where the single-task, single-focus movement can have a powerful change in your life. Remember that society is making us all into multitaskers by dividing and conquering our attention (the quintessential example being advertising).
There is however another stream of activities where multitasking can be a really useful thing – and this is when you are doing mundane activities. Think stuff like chores, watching TV or waiting in line. Here, you can become more efficient by “grouting” these activities with something useful like reading or listening to a book, doing some exercise, or responding to straightforward emails. The key being to recognise and take advantage of these opportunities.
I subscribe to the belief that the most productive people don’t necessarily work harder than the average person, they are simply smarter about what they do and when.