well, in my experience the green + button behaviour is pretty consistent and predictable...with some exceptions.
usually, all it does is toggling between two states:
1) the last (user-specified) window-state and 2) some system/app defined optimal setting.
this last-/user-specified setting (1) is set whenever a window first opens or when you move or resize a window.
the 'optimal' setting (2) is controlled by the OS and/or the developer.
if she (the dev) doesn't respond to the clicking-the-green-button-event, the action defaults to trying to go as fullscreen as possible, or to the biggest size possible for that window. and back to the previous state when clicked again.
this 'optimal' setting is indeed not always very transparant, and certainly doesn't always mean 'fullscreen'.
as mentioned above, the Finder for instance will just resize and relocate a window to optimally fit it's content and display on screen, which usually is not fullscreen. i use the green button for exactly this reason all the time.
clicking the button again will usually toggle the window back to it's original state, although there seems to be some kind of algorithm behind the mechanism to prevent user-unfriendly window layouts.
i admit that this sometimes also makes me too wonder...
the event of clicking the green + button is something developers can capture and react-on in their software, and the implementation in different software varies.
i understand people may considered this as inconsistent, but i think if you're aware of that, it's not. it's part of the behaviour of an app. each app has it's own real estate requirements..
generally it's a feature i use all the time, and i just got used to it's behaviour...much in the same way how i also don't exactly understand how most people around me exactly function ..
BTW:
Yes, I've used the Option-Close-button ... although I wasn't aware that it would maximize all of the windows for that application in OS X.
..as mikuro wrote, the option key makes the zoom-action be performed on -ALL- windows of a certain app, but that is also true for the other buttons (close and minimize). and it becomes even more interesting when you also hold the shift-key to make that all happen in slowmotion...
...and it becomes even more interesting when you then also kill the dock while this all takes place... (hihi)
check this:
http://www.arri.nl/gui_fuck.mov
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- if the stream doesn't work, make sure to have qt-transport settings in qt-system-prefs set to http
- credits for hacking coregraphics :
http://www.atzenbeck.de/research/wildWindows/ and others
- and
http://usemedia.com/ for the rotating duck