Essentially, I buy knives to use. There are a couple exceptions tho.
When SMKW had the CRKT Mirages on sale for $10 apiece, I bought 6, 2 of each size and plain edges and, I think, combo edges. I know they'll never increase much in value, but thought that someday I might try to make a little exhibit of/for them. I've always loved the blade shape, even tho the handle isn't as ergonomic as one could wish.
When I first heard that the CRKT Apaches were going to be discontinued, I wanted to buy one before they were gone. I can't remember all the details as to why now, but I bought a black-bladed, combo-edged copy. I don't much care for combo edges, and I know that most blade coatings get to looking like hell after some use. So, was surprised as the dickens when I got the knife how beautiful it seemed to me. I know I'm not in a large group feeling that way about that knife. But, I decided to keep it new, and bought a regular, PE model to use.
All my other knives I use to at least some degree. I'm so into my favorites now, that the others don't get much carry time.