I've used i3 quite a bit, but to this day I still don't get where one would want a more complex window management than your standard L/R split? If I need more complexity than that, it's inevitably on the command line, and I'm in tmux anyway. I'd love to see a workflow with more splits where one wasn't on the command line.

Sometimes content is better as a top/bottom split (e.g., long lines). The ability to "rotate" the layout by 90° with a single keybind is very useful (I use XMonad myself). I can also put multiple windows on the "main" side and rotate between 2 "stable" and a larger set of "smaller" windows. This is handy when juggling RDP into N machines while waiting for Visual Studio or Xcode installations to do their thing.

I also enjoy the simple keybinds I have to sling windows between monitors and workspaces easily. I have no idea how I'd do that with any of the tools on macOS or Windows in a maintainable way (XMonad's configuration lets me cartesian product between (noun, key) and (verb, modifier) lists to make things very consistent).