I never use them. I wonder if it's just me. Early on they are too good to use, and later on, it makes me think it's not worth removing something like a gladiator belt, grail locket, evergreen, etc for.
I abused the hell out of the type that restores CP on revive in one particular fight and generally have one on a party member with a healing/Max Guard S-Craft because that can turn a fight around if things go bad. Once CS1 rolled around and you could get the same effect on Master Quartz, I generally used that instead.
Oh, and it's kind of funny to abuse auto-revive options in some unwinnable fights just to see how badly the computer will cheat to ensure you lose.
Ahh. Yeah in CS2 when you fight Rufus, I made him spam his S-craft 4 times in a row with 0 delay. don't remember what I did to do that but yeahhh...
I think I should use them as soon as I get them, and replace them when I get the superior options, and not worry a bout 'saving them' for a better moment.