macOS has a single menubar that changes, depending on which app is in the foreground. Being able to interact with it is going to be critical for building any real-world Mac app.
I suspect that Windows and Linux have libraries for building and interacting with per-window menubars, and I would think that interacting with that would also be critical for building any real-world Windows/Linux apps.
In macOS, the ability to not show up in ⌘-TAB or on the menu-bar would also be useful.
For example, if you're simulating multiple top-level windows by running multiple instances of your app, each with its own top-level window, you'd only want one of them to show up in the ⌘-TAB list, or on the menubar. Windows and Linux would have similar wants.
You'd probably also need this if you want to write a gadget that draws on the macOS menu-bar, a-la iStat Menus (https://bjango.com/mac/istatmenus/). (This is a very different kind of menubar interaction and may deserve its own ticket.)