I'll just add that this feature existed in Windows 7, so blame/credit can go a little further back
I'm not a huge fan of the feature myself, but only due to having a 30" monitor, so I almost NEVER have any full-screen windows. It's one of the reasons I had zero interest in the "Metro" UI for Windows 8.
There's on component of this feature that I do use from time to time, but mostly on other people's computers. We've already covered how dragging the window to the top of the screen will maximize it, and dragging it to the left or right edge will dock it to that half. The one I use - particularly in the task manager - is where you click and drag only the top edge of a window up to the top of the screen, and that snaps it into filling the height of the screen. Like I said, I use this for the task manager so I can see as many of the running processes at once as possible. There are a couple other instances where it can be handy too, almost always involving long lists of things.