The main takeaway (which should be obvious) is that you should test your navigation and probably test it a lot. It is very important and it does matter. I've caught myself thinking of it as a pesky thing and I'm not a designer and usually don't optimize for pretty because well I'm not good at it. But the fact of the matter (imo) is that focusing on content and navigation until you get them perfect is the best approach.
"Silly" exercises like card sorting early with potential users (or regularly for an existing site) are actually pretty solid methods to improve sites and apps greatly.
