On my desk at work I’ve got a Windows box, my MacBook Pro connected to an external display, and my iPad Pro. I’ll use whichever best suits what I’m doing.
For instance, our work email and calendaring is so locked down that I can’t put it on the Mac except through the Office 365 web client, and I don’t want to put any of my personal calendars on my work PC, so the iPad is the only device that has both personal and work calendars on it. I do a lot of my calendaring on the iPad. Or I may have handwritten notes in Goodnotes up on my iPad while I work on something in iA Writer on the Mac. I also have some Shortcuts on iOS to set up complicated projects in OmniFocus, so I’ll use the iPad for that.
Now, thanks to the large screen and better ergonomics the Mac is my first choice for a much greater portion of my desk bound tasks than the iPad is, but for some things the iPad is better and it’s right there, so why wouldn’t I use it?