There’s no such thing as useless knowledge—only knowledge that relies on very specific situations. Which is why, in the event of a horrible Mad Max future, you might want to learn how to make a bow and arrow using no modern tools whatsoever.
Sure, making weaponry with access to a bandsaw, a lather, or hell, even some chisels would be orders of magnitude easier. And there’s no reason to assume in a semi-apocalyptic event that any of those things would disappear (maybe electricity, but hey—chisels). The point is, Primitive Technology is really good at what he does and it’s impressive to see someone make stuff the way your great-great-great-great-great-great-great-great-great-great-great-great-great-grandparents might have.
As a bonus he shows how to put fletching on arrows, and make a small quiver to hold them. Hopefully, the deer and birds of our shithole future won’t be too irradiated to eat.