Zoom tries to remove the scroll bars. It makes the window big enough so that the scroll bars disappear. If there are no scrollbars and the main content just automatically resizes with the window (e.g. in Aperture) it is equivalent to the maximize button.

The biggest problem with that is that developers make it work inconsistently.

Browse around iTunes until you find a track that doesn't quite fit horizontally. Click the "zoom" button, to make the window big enough. Oh wait, it doesn't.

If by "developers" you mean "Apple" then yes. I never use the "zoom" button because it exhibits apparently random behaviour.

Agreed. It's one of those "we'll figure this out later" things from the late 90's without any real programmatic constraints that led to a mishmash of pointless and unexpected behavior.

I personally can't come up with a good reason not to just remove the green ball entirely.

So the issue is iTunes, not the green button? And admittedly itunes behaviour is very well known, it's hardly surprising.

I completely agree with you. Don’t be so aggressive, be nice!

Apple should remove the zoom button. It’s not necessary, more confusing than anything.