As the post-PC era looms, I think that the better question is why anyone needs a desktop *or* a notebook? Most people can get by with a smartphone or tablet.
At work, I opted for a desktop computer (iMac) because I work in IT and sit at a desk 100% of the time. A side benefit of having a desktop PC at the office is that I can't bring work home at the end of the day.
At home, my personal computer is an i9 CPU Macbook Pro. Thanks to COVID-geddon, I'm also using it for work because WFH.
Going back to work is going to be fun, mostly because I haven't run updates on my office desktop since last October.....