The Zoom button, or very commonly incorrectly called the Maximize button, has become a point of confusion for switchers and new users alike. Most switchers expect the Maximize button behavior of taking up the whole screen, hence the nomenclature problem. I regularly take it upon myself to clarify, but lately, it’s become a losing battle.
The moment I explain the proper operation (resizing just enough to expose all the content of the window), exceptions get pointed out. That list of exceptions isn’t restricted to third party applications. Apple is increasingly changing the behavior.
At first it was just iTunes with switching between normal and mini player modes (which, oddly enough isn’t tied to a title bar button in Windows). The abuse I’ve most recently been made aware of is the Calculator. The comments at the macosxhints.com article do point out a couple quotes from Apple’s Human Interface Guidelines (HIG).
Your application also sets the values for the initial size and position of a window, called the standard state. Don’t assume that the standard state should be as large as possible; some monitors are much larger than the useful size for a window.
and
The user can toggle between the standard state and the user state by clicking the zoom button.
While the latter seems to hint vaguely about standard and user states, the former refers to window size and position. The Zoom button has become such a confused interface element that users can’t count on consistent behavior between applications. Without the trust that the button will have an expected effect, users will be forced to pass it by rather than try it and hope that it does what they expect.
A return to consistency is needed.
One of the most helpful ways to use the Zoom button is when, for one reason or another, a window is larger than the screen, so that you cannot reach the lower right-hand corner to resize it. A click on the little green button and the window is once again displayed within the bounds of the screen and can be manipulated manually. This is, for instance, much easier than increasing the monitor resolution temporarily to get at the over-sized window.
To be honest, I never knew that the correct name for the function was "Zoom" (with a Windows background I've been calling it Maximise as well). However, I can really appreciate that the expected function of this button is to only show as much data as is needed rather than the Windows approach of filling the screen no matter how much of a waste of space this action is (actually, that phrase applies pretty much to Windows as a whole...). A consistent approach to implementing this function would definitely be preferred.
One of the main functions of the Zoom button that I used was to make a Finder Window zoom out to encompass all the icons in the window (so you didn't need to scroll up or down, left or right).
The OS X Finder doesn't do this reliably - in fact, I think it only did it right in the last version upgrade of 10.2 - then it was broken again in 10.3. Bad for a neatnik like me :(
When are they going to fix the Finder??