In the mainstream we often see multitasking being treated as a skill. People want to get good at it! The term multitasking came up in the 1960s to describe a computer. But even those very computers were not doing multitasking, they were switching between tasks quickly. You can not do two things at a time optimally.
To do any task effectively focus is the number one thing. When we begin a task, we take time to get in the zone, we have to update the context and rules of it. During multitasking, we are switching between one task with others. While doing it we are losing time and energy. More you switch more time you lose. Instead, do them separately.
But then you would say, "Improveistic! I regularly do multitasking like watching TV while folding clothes or walking while talking on the phone." Tasks like walking and watching TV do not require enough focus hence you can pair them with some other tasks. Let's say you are walking on a tightrope, you would stop talking as soon as you start walking because you need to focus.
Lesson from: The One Thing