I have a really nice slide-rule I bought awhile back. It's fully functional and that was an important part of why I bought it. In spite of that, I still grab a calculator when I want to do a calculation more complicated than I can do mentally. But I like having it and I like that it works even if I never actually use it for anything practical. It's possible that there could be a confluence of circumstances such that I might actually NEED it someday for some calculations, but that's not why I bought it. Sometimes I just take it out and play with it awhile, do a few calculations for fun and then put it back away. Is it practical? Well, it could be but the circumstances that would cause me to reach for it instead of the calculator would be unlikely.
I have my great-grandfather's pistol. I also have ammo for it but I don't intend to ever shoot it. I like the fact that it's fully functional and that I could shoot it if I wanted to. I suppose it's possible (though not that likely since I have other guns) that I might have to use it someday, but that's not why I have it. I do take it out from time to time to check it and just to handle it. The fact that it's not as useful as some of my other guns doesn't bother me. If I had to deactivate it for some reason at some point in the future, that would really irritate me and would diminish my "joy of ownership" even though I have no real plans to make use of its functionality. Is it practical? That's not why I own it, but I suppose it's as practical for its intended use as it was when my great-grandfather owned it.
Awhile back, I got a large double-edged knife. It's fully functional, good handle geometry, a functional guard, good steel and a nice grind. The blade style is really good for a self-defense knife. I could carry it legally where I live--it's possible I might someday--and I suppose there could be some situation arise where I might use it for self-defense (that's about all it would really be good for given it's design), but that's not really the reason I bought it. I just like it. I like that it's fully functional, that I could use it if I needed to and the fact that I might never carry it or actually "use" it for the purpose it was designed for doesn't really diminish the pleasure of owning it. I get it out and handle it once in awhile, make sure it's sharp and in good condition.
I've got a really nice high-end compass even though a GPS unit would be far more practical and more compact. But I like the compass. Maybe I'll actually use it for something practical one day (it's certainly functional and I know how to use it) but I doubt I ever will. Even if I never do, I'll still be glad I own it.
I don't have a really nice functional sword but I would like to get one and I may someday. If I did, there's a distinct possibility I would never use it for anything at all remotely practical, but I would still want it to be fully functional.