Even those people that really use their knives. Have knives they don’t use. Also we take pictures of them when they were new.
To answer the original question. For me its a tool, but also a habit. I feel naked without a knife.
Personally, I enjoy seeing and taking pictures of knives that have done some living. To me, most of the examples of a given model start out looking pretty much all the same, it's the markings of the lives they've led that really does it for me, but to each their own.
Some of mine get used more than others, but they all get used. I couldn't bear owning a "safe queen." I didn't even like typing it just now - gives me the willies.
I feel the same with guns. The following is a paraphrased excerpt of a conversation with a good friend of mine as he was giving me a couple pistols that had been in his family for generations (he was moving to a city where they were not welcome):
Me: You know I'm going to shoot these, right?
Him: Yes, that's why I'm giving them to you.
Me: Okay, cool. As long as we're on the same page.
Him: Well, I think it would be sad if they just hung on a wall forever.
Me: Yeah, me too. That won't happen here.
Him: Thanks, man.
Me: No, thank you.
Recycled picture of some knives in various stages of life: