That doesn't work on OS X 10.11. Just tried it - Nothing happens. You need a tool like Spectacle/Magnet (or potentially Hamerspoon, haven't tried it yet) - I don't know of any way to maximize a screen using basic OS X 10.11 interface, which is bizarre if you think about it.
It works just fine on OS X 10.11 [1]. Holding down 'option' while you hover over the green traffic light icon changes the glyph to a '+'. Clicking it maximises the window.
It really doesn't. I just did so in Safari. Held the Option key, hovered over the green traffic light, and it first reduced the size of the screen. I clicked on it again, and it filled the screen vertically, but not horizontally. Still need to use Magnet/Spectacle to maximize my window.
I think the problem really is Apple's use of the term "maximise" doesn't mean what it does on other platforms, and really it's a misnomer entirely. "Optimise" would be a better adjective, and its behaviour differs slightly depending on the app. For example, in Safari it'll resize the browser window to what it thinks is best for the content you're viewing.
Thankfully, tools like you've discovered address this behaviour and add a lot of other useful window management features anyway.
The weird thing is the behavior doesn't seem to be predictable. I just maximized my screen with Magnet (cause window to stretch out both horizontally and vertically), then I option-clicked on the Green Streetlight - Nothing happened. Then I made the window a bit narrower. Clicked again. Nothing happened. Then I made it a bit shorter. Clicked Again - Window stretched up to top, but didn't change width. Made it narrower. Clicked again. Window returned to previous width. Clicked again, this time returned to the same narrower size as one step previous.
It seems like the Option+Click on the streetlight is kind of like a toggle of the last two previous sizes, but not always - sometimes it stretches to the top, sometimes it doesn't do anything.
I've been a dedicated OS X user since 10.3 - and, despite spending 15-20 minutes at a stretch every year or so (such as tonight) - I've never really understood what the green button is supposed to do. I kind of find it amazing that such a horribly inconsistent user interface control has persisted for 15+ years.
But yet - Magnet (much like Spectacle before it) does exactly what I want. Ctrl+Option+Enter = Maximize window (which is exactly what I bet 99% of people want the Green Button to do)
Did you try shift or alt, or combinations of those? I'm pretty sure it's been hidden in OSX for a while, but I think the shortcuts were changed at some point.
