We are so accustomed to multitasking that we even forget how it decreases our productivity.
You have it well explained here.

A single-tasking boss only ever has meetings with departments on the same floor as each other, because their duties are very similar.

A multi-tasking boss has meetings with people from all different floors regardless of their job title or role in the company.

I attended a seminar once on personal development where the speaker told us to do something i will never forget about multitasking and single tasking.
He told us to do two exercises while he timed.

1. Write ABCD..Z while writing a corresponding number on top of the letter.
   That is write A and write 1 on top and B and 2 on top,until you finish the alphabet.
2. Write out ABCD..Z separately and then after write corresponding figures on top of the Letters.

The results amazed everyone in attendance.
We spent much time doing exercise 1 and very little time doing exercise 2.
That exercise we did showed us the benefit of single tasking and the the demerits of multitasking.
Thanks for this series.