Just to add, holding down the Option key while pressing it alters it behavior to be a maximize button in most apps. Some apps (like Chrome) use the Shift key to

Just to add, holding down the Option key while pressing it alters it behavior to be a maximize button in most apps. Some apps (like Chrome) use the Shift key to get this behavior instead. I would like things to be more consistent. In fact, if I were in charge, I would want this button to be a maximize button by default, while using the Option (i.e. Alt) key should alter the behavior to the second option which is to resize to the best fit for window content. But this may need debate since now we have fullscreen mode for apps in Lion.