I've just spent some time fighting with the hinge in the image below and finally worked out how it works. There is one part of it that's still a mystery and in the documentation it's called the Panel Release Button. It's the button marked with an R just above and to the right of the Horizontal Adjustment Screw. Anybody know what this does?
To directly answer the question: The panel release allows the hinge to be separated into two parts, so the door can be dismounted without removing the screws and later snapped back into position. (Essentially, it gives you the same capability that removing the hinge pin would in a more traditional design.)
This is an anderson series 400 hinge that limits or adjusts the swing opening on French type windows. Here is a link to the Anderson service guide that explains the functions and how to use the adjustments. http://www.andersenwindows.com/-/media/aw/files/technical-docs/service-guide/serviceguide-0005225.pdf
