Not necessarily for self defense, but just as a matter of habit and custom. I've carried a Stockman style pocket knife (mostly Imperial, Old Henry and/or Old Timer) for almost my entire life. I never leave home without it, and it has "saved my bacon" in numerous ways over the years. For decades I've also kept a Leatherman Wave in my briefcase for the odd repair and/or plier needs, but the pocket knife is always on my person.
It's a habit inherited from my dad and grandfather's time and was solidly ingrained by the Boy Scouts back in my day -- "Be Prepared!" In fact many of the boys I went to grade school with (and later High School years) carried a pocket knife. How times have changed!! Current carry is an Imperial and Old Timer.
When hunting season starts I have two knives in the truck and pack. A Buck fixed blade for general cutting and an Old Timer Sharpfinger used only for skinning.