Did you mean FFVI? I found Osmose ('Psych') to be a useful way for Rydia to gain back MP in order to continuously cast her most powerful attacks. Most enemies in FFIV have MP and you can generally get the cost of Leviathan back in 1-2 rounds. 1-2 Osmoses +Levia is much better than three of her weak normal attacks.
Quake was a cheap attack all spell in FFIV that I used on occasion.
Mini was useful in one FF game. You had to use it to proceed.
I have never used Pig once in FFIV other than to mess around. Why did Pig status even exist? Toad was slightly more useful since there were those witches in the Sylph cave that would always Toad you.
Rasp is probably the most useless spell ever, though. I'm not even sure what it actually did.