Wow. I wonder what most people's employers would think nowadays if their employees stated that "nobody really needs a multitasking OS and most people won't ever use more than one program at a time." Where I work, that would pretty much be grounds for dismissal.
So you mean there's no need to download or install a file in the background while you write an email to someone? No need to generate a PDF while doing something else? No need to make edits to video while rendering an image sequence in another app?, No need to work in a spreadsheet or word processor while the computer does a virus scan or indexes files? No need to have someone run a remote desktop connection to your machine while showing them something in another app? No need to have two audio apps share information with one-another while playing a sequence? No need to run a video/screen capture app while running another program? I could go on, but I think just about everyone on this forum can find multiple cases in which they made good use of a multitasking OS to save time and do things more efficiently.