I've literally never used one of these. I've never even seen anyone else use them. They can't be used in battle, and they can't be used on yourself. If you're in a party out in the field, then chances are, you won't be dying any time soon.

I recall one FF game treating these as more expensive and special items, although I cannot remember which. It'd be interesting to see if SE made a self-inflicted version that activated upon death and made them much, much more rare. That would make them worth something, as well as have an interesting effect on the market board.