Jared Spool talks about "visual disorientation," a designer's technique for evaluating your design work in the middle of a process. It's certainly common to see designer's tack up pieces of paper around their project space, e.g. schematics, pictures with references to other objects that provide inspiration, etc. Hunkering, however, is more of a technique to create disorientation and change in one's perspective momentarily, to assess what you've done.
Visual disorientation is a fast way to identify the places where things don't quite match up. Hunkering, in its simplest form, is a chance to force a moment of visual disorientation -- to make things seem foreign and out of place.
Hunkering gives the designer a chance to get lost in the reality of their design. Like visiting a vacation spot you've only seen pictures of, the initial impression takes a little getting used to. Then, once you've had a chance to orient yourself, to find the familiar elements you were expecting and place them relative to each other, the vacation spot becomes more comfortable. But in those places where the pictures didn't match the reality, that's what will stand out.
Hunkering, and its subsequent visual disorientation, can be a crucial tool for the designer. Used properly, it can prevent downstream errors and give new insights into the final results.
Some of the ways we may hunker is by simulating walkthroughs, prototyping, or rendering parts of rough ideas in higher fidelity. It's a process of: stepping back, looking, and seeing the forest for the trees; thinking, questioning, and orienting; and finally returning from the mountain top view to start back into work.