I think just about every FF probably has at least one of these. There's a new ability you get and you might try it once and never use it again. Looking back I think some of these could've been worked to have been useful or at least more useful than they were.
Some of you might've used Card in VIII or Thievery in IX, but have you ever relied upon Mad Rush in FFVIII?
The Summons in XII?
Charge! in IX?
I think some people would've used Charge if it had worked differently. In the game it makes all of your near death party members attack at once. It would've been better if it allowed all allies to attack at once if they had full ATB bars. Also with IX I think that might've been when the breaks were first introduced. I never felt compelled to use them in that game. The couple of times that I did use them it missed. Then there's the really useless Thunder Slash that never hits. It does work properly for AI Beatrix though.
Also on my first playthrough of IV I got the summon Goblin. As soon as I used it I wondered why such a weak summon is in the game.