I usually carry a knife for utility purposes as part of my leatherman. Comes in handy for cutting all kinds of things and as a "somewhat" screwdriver if needed. The other attachments get used but the knife seems to rule the day.
When I'm hunting I carry a different knife, one that's all purpose for gutting and skinning.
I don't carry a knife for protection. I have a tire knocker in my car and if I'm out and about I carry a an extendable baton.