The green button isn't a maximize button, it's a full screen button. Full screen on macOS is a separate virtual desktop, so you can't just quickly bring up another window to reference something. Some apps simplify/hide their UI in full screen mode, and until recently, the menu bar would always auto-hide in full screen (it's configurable now).
There's also Zoom, activated by option-clicking the green button. This resizes the window to the app's preferred size, which is random, and usually not the full screen (e.g. full screen height but whatever width it had before).
Turns out operating systems named "Windows" are much better at window management. (The maximizing stuff is one issue, the application-first model is another.)
I'm still pissed at Apple for changing the default behavior of the green traffic light from Zoom to Full Screen. I never want to use Full Screen, and when they introduced it in Lion with a dedicated button I was content to ignore it. Even though I've developed muscle memory to hold down option every time I hit the green traffic light there's still times where I forget, let go early, etc. and I end up fullscreening the damned window instead and curse under my breath.
I never minded the application-specific Zoom behavior in macOS, in fact I find it much saner than Windows where you often end up with dead space inside an Application doing nothing. Safari pretty intelligently figures out the maximum horizontal width of a page before padding would be applied and resizes to that when zooming unless your window is already beyond that breakpoint, for example. Same thing with Word, for example. I don't want to see a bunch of dead space on my screen, I just want to show the maximum amount of content my application+display can show at once. (This is where I really dislike the change to the green traffic light, I don't want Window-like behavior on a Mac)
There's also Zoom, activated by option-clicking the green button. This resizes the window to the app's preferred size, which is random, and usually not the full screen (e.g. full screen height but whatever width it had before).
Turns out operating systems named "Windows" are much better at window management. (The maximizing stuff is one issue, the application-first model is another.)