The first most important thing about a project is that it come out right in the end. In order for this to happen, gauge can be really important or completely irrelevant.
Harper’s situation shows how funny gauge can be. Even though almost all of her project makes a nice fabric on one needle, the little bit that is the important design detail insisted on a larger needle. This is not a democracy. In order for that part to work out, the whole thing should be done on the larger needle, and the rest of the fabric would come out just fine.
In another situation where gauge made a difference, a large woman wanted to knit a simple sweater on large needles. She had a pattern she liked, but it was too small for her and worked at a smaller gauge (about 3 or 3½ stitches per inch). She wanted to work on 15’s at about 2 stitches per inch. So she picked out some yarn (a double strand of worsted weight), and we figured out that the pattern should work for her if she followed the instructions for the petite size and kept an eye on how long she wanted the pieces to be. By golly, it worked. So gauge information can be useful for something.