Goethe kept some of his information in boxes, papers loosely held together by strings, and as stuff thrown into drawers without any apparent order. He often went back to this "rummage box" in order to work these materials into his publications. His Faust clearly originated in this way. He himself called the drama suggestively "a family of sponges."
Christoph Martin Wieland, another poet in Weimar found that "Goethe work in general in such a fashion that he "works out individual parts and then very loosely connects them with each other."
If this sounds very much like writing in chunks or the fieldstone method it is because it is similar.
Wieland did not think that this method always led to good results. Rather, it often led to "remarkable unevenness." Whether or not Wieland's criticism is apt, one might wonder whether unevenness is essential to the method or an accidental feature of a writer's habits. I would guess that it is the latter. I also think that Wieland exaggerates the unevenness. Even though Faust II is remarkably uneven, other works are composed rather rigorously.
1. See also Thomas Mann, "On Geoethe's Faust."