Make the green full screen window icon on Yosemite maximize windows
As the below mentioned solution is application-based (i.e. only works for apps like Google Chrome), another way to approach this problem is to ignore the maximize button entirely and to install the open source app spectacle which offers the keyboard shortcut:
⌘ + ⌥ + F
It also has some other nice features, too. And it works for all apps.
In order to maximize the window so that it fills the visible window content, use:
⌥ + Click on green icon
In order to maximize the window both in width and height to the current desktop for applications like Google Chrome use:
⌥ + ⇧ + Click on green icon
You notice the change of behaviour of the button in the way it changes its content from two the arrows to a plus sign.
Zoom function can now be performed more easily — by double-clicking window title. You don't need to precisely aim at the small green button anymore, which I believe is the reason it has been converted into full screen button by default.
If you hold the shift key and double-click the window title Applications that use "smart zoom" will be forced to do full screen zoom. Smart zoom was a (much missed) OS X window behavior where, rather than fill all of an immense display, the window would enlarge based on its "needs". Apple removed smart zoom behavior form its own apps, but Chrome still does this.
So, in general, make the painful switch to working with the title bar and ignore the green button except for the rare times you truly want full screen. If you get 'smart zoom' and want to fill screen instead, repeat but hold shift key.
Hold option and left click the green button to have it maximize but not go to full screen.
@Wladimir Palant has a great solution, using BetterTouchTool to reassign the role of the green button. Works for me!
Note: @Wladimir's answer actually solves this question, not the one he posted in.
Disable option "Double-click a window's title bar to minimize" in Settings -> Dock. Now you can use double click on the window's title to maximize it.