See many of these threads...
Firstly, it purely depends on that person's requirements.
When I was younger I had the 17" PowerBook, followed by the 17" MacBook Pro. I had both devices purely for recreation and high school work. I just always wanted the top of the line devices.
I'm now in a job that provides a Windows laptop but also encourages using your own devices when you can and therefore I have work specific apps on both my iPhone and iPP 9.7".
I use my Windows laptop when in the office. Always. Mostly for emails and meetings requiring screensharing. Although the shared is mostly of Microsoft Office documents, so nothing extreme.
I use my iPP at work for note taking when in meetings. This has totally changed how I work. It's a simple use of the iPP, but I also have the additional functionality of the work provided apps, allowing me to review & edit office documents, dial into WebEx meetings, view our internal intranet. Nothing I could have down when at external meetings previously when taking a laptop isn't appropriate.
My iPP is my only personal computer, I no longer have a MacOS device.
I'm able to scan documents, print, touch up photos, mash together videos with titles and chapters, use Microsoft Office, play the occasional game, view content via Netflix, local catchup apps, YouTube, make payments, everything I need to do, with my iPad! In fact, if I was in a position where I could only afford 1 device, I could do everything I've mentioned with my iPhone 7 Plus. Something I have on me all the time, everyday, always connected to the internet.
I totally understand that others will require the additional workhorse of a desktop based operating system but for most, including myself, iOS is perfect.
I'll soon be upgrading my iPP to the 2nd gen 12.9" as I've decided the extra real estate is worthwhile as it is my main computing machine. I also find myself in places where I'm stopping over night and the iPad is my main device, having the bigger display for content will be great.