For work, it’s usually IDE on the right (my larger screen) and a live build of the thing I’m working with on the left (a laptop screen). Though it varies a lot throughout the day. Primary screen gets the app that needs most scrutiny, small screen gets auxilliary things like passive communication apps or reference materials.
For home use, where I have two monitors of equal size, it’s usually Discord on one screen and a web browser on the other. Comms on the left and active task on the right.
I don’t see a use case in my workflow for a third screen, especially not one that is a weird size or is in portrait orientation. But if one was simply bestowed upon me, I’m sure I’d find something to do with it sooner or later. There was a time where I though two monitors was overrated, I’m sure I can adapt my opinion again for 3+.