This morning, while sipping my favorite green tea at home, I automatically checked my smartphone for office mail. Although there was no reason for not enjoying the morning time with self, sub-consciously an escalation thread was happening in my mind and my intention was to check the current status of that escalation, which was occupying a portion of my mind concerning one of my projects. While going through the various threads of communication, and sensing some anxiety entering my mind, I suddenly wondered what I was doing during the best time of my day.
This is nowadays very common, a recurring instance that perhaps many of us experience.
The competitive world, long working hours, rising expectations on the personal and professional fronts, work pressures and personal aspirations; all demand a multi-tasking of the mind. All of us are used to multi-tasking, and it is a quality without which we cannot think of completing our day. If we take time to notice, we will find out how frequently we multi-task.
When we drive vehicles, text, use computers, make phone calls and attend meetings, we are subconsciously juggling various tasks and ranking them based on their perceived order of importance. 
Some other examples include drafting a mail while attending a call, listening to music while working on a document, and working on more than one project/task at a time like driving and attending a call (which is proven to be very dangerous).
Understanding the importance and high usage of multi-tasking in our daily lives, I researched the subject and was amazed to find out the following facts:
Multi-tasking is a computer industry term, which refers to the special ability of microprocessors to perform several tasks in parallel by dividing the RAM (Random Access Memory) into various parts (Reference: Wikipedia). Nowadays, multi-tasking seems to be an important KRA (Key Result Area) of the human mind which is actually like a computer where the same performance is expected of it.
Computers multi-task. Humans don't. A computer's operating system enables it to perform more than one task at a time without losing data or failing to process information. The human brain doesn’t work this way. What we call "multi-tasking" is actually "serial tasking" or "task-switching" — moving from one task to another in rapid succession.
Our ability to focus on different things is one of the strengths of our truly incredible minds. It's a skill we would definitely not want to lose. However, psychologists and neurobiologists have both shown that we pay a price when we multi-task. Since the depth of our attention governs the depth of our memory and thought, multi-tasking can reduce our ability to understand and learn. While we are able to do more when we multi-task, we learn less. As we juggle an increasingly large number of different tasks, we start to pay a price in our cognition.
There have been studies to prove that the human brain is not meant for multi-tasking, more often called ‘brain juggling’ in psychological terms. Robert Rogers, Ph. D, and Stephen Monsell, D. Phil found that on switching between two tasks, the human brain comes across two types of resistance - firstly - to adjust the mental controls to attune to the new task, and secondly - to stop the mental controls from processing the first task. The cost of switching tasks is always higher than repeating the same task. It is approximately 40%, which cannot be neglected.
As the task becomes more complex, the cost of switching between tasks gets higher. Complex tasks always require deep research, and the deeper the mind goes into a task, the more time it would take to come out of that task. In this scenario, switching between two tasks becomes tough.
When you’re trying to accomplish two dissimilar tasks, each one requiring some level of consideration and attention, multi-tasking falls apart. Your brain just can’t take in and process two simultaneous, separate streams of information and encode them fully into short-term memory. When information doesn’t make it into short-term memory, it can’t be transferred into long-term memory for recall later. 
Multi-tasking involves engaging in two tasks simultaneously. But here's the catch. It's only possible if two conditions are met: 1) at least one of the tasks is so well learned as to be automatic, meaning no focus or thought is necessary to engage in the task (e.g., walking or eating), and 2) they involve different types of brain processing. For example, you can read effectively while listening to classical music because reading comprehension and processing instrumental music engage different parts of the brain. However, your ability to retain information while reading and listening to music with lyrics declines significantly because both tasks activate the language center of the brain. 
Multi-tasking may seem to be efficient at surface but in reality it costs more, and also affects the quality while increasing error. For example, using a cell phone while driving and losing by a second in task switching can cost one’s life, which cannot be compensated by any means.
We are in control of the information we receive. By filtering the flow of data and registering what is really important for us, we can develop the practice to improve focus in our everyday lives. However, reducing information overload doesn't require blocking or abandoning technological tools, which is kind of a necessity in today’s world. Instead, we need to find effective ways to accept only relevant information and discard or minimize superficial information. The best way to do this is through awareness of the danger of long term multi-tasking through which we can achieve a more favorable and effective environment at home or the workplace. 
Wonderfully, this piece of information can be used in understanding user psychology in the field of user experience design. We are now building applications in bulk for smart phones, tablets and devices on the move. Keeping the effect of multi-tasking in mind, we can understand how much attention to detail a user exerts on applications on such devices. These apps must be ’brain-dead simple’ to work well.
The adaptive quality of the human mind can be used in a more constructive way by focusing its massive energy on a task to perfect completion or can be used in a dissipative way to lose its energy through multi-tasking. The choice is ours.