Updated June 15th, 2019.
Click the green zoom button in a Mac window and the window goes full screen– and it’s so full-screen that the menu bar’s taken away. That’s not what most of us expect– especially if you’re used to the way that button used to work (it zoomed, but it left the menu bar alone).
Also, it’s hard to get out of the full-screen mode, unless you know how. There are two ways. The first: try tapping the Escape key. The second: move the cursor to the top edge of the screen. The menu bar should appear, and the buttons at the top left of the window will appear also. Click the green button again. Ah, that’s better.
Turns out you can make the green button behave the zoom-but-don’t-hide-the-menu-bar way by holding the Option key down while you click it. Apple gives you a tiny visual clue that holding the Option key will give you a different result– try hovering over the green button with and without the Option key held down.
Sometimes bigger isn’t better. This is one of those times.
BONUS: see this article for an even better way to resize your windows.