It’s a lot of trial and error over many projects that will give you intuition on these things!
I grew the selection to the center of the crease between sections because otherwise the black that we apply for the material would have a gap in it and wouldn’t reach all the way to the crease. Similar to that, I wanted the sharp part to run all the way to the center of the intersection, and that one was right in the intersection. It could have been any of those three similar edges though that radiate out. When you have these questions I would recommend trying them out and seeing what happens! Sometimes there are many ways to accomplish the same thing and it doesn’t really matter, but other times you’ll see how things turn out differently and then will get a better intuition as to why we did it that way.
