I carry a big knife with a 9 inch blade mostly because it looks friggin cool.
I'm a /trv/ler first and foremost before being an /out/lander, and when you're surrounded by angry locals who only want to kill you and get all your gear, carrying knives bigger than theirs and proudly wearing them, strapped to your chest where everyone can see them, helps quite a lot. It makes the difference between locals coming to harrass you and locals keeping at bay and avoiding eye contact.
It's also a bit more acceptable to carry a knife, no matter how large, rather than an axe. Not sure why, maybe because an axe may be a much more efficient weapon or something. You can definitely be forbidden to go to certain places because you have a knife that's too large, but then you definitely can't go anywhere with an axe. Thus I've learned through the years to leave my mighty Gransfors Bruks axe at home. It's also long enough to pass as a machete, and machetes can in some places be more acceptable than knifes.
I have actually little use for an axe, and even less for a short knife. I have a small and light dull edge knife for cooking, I don't spear fish, I don't build shelters, I don't carve wood, I don't dig much holes, I don't gut animals...
What I need above all is to be able to quickly grab it and perform a large sslah with it, whether it is to attack someone or a wild beast, cut a rope or net, break a window, use it as an emergency pry bar and the like. I actually have one with a few serrations for some of those reasons.
I don't really see much uses for a large knife as a innawoods/survival knife, but that's not what everyone does.
