I was wondering if you keep your characters sole identity by passing on some ability slots??
Like for example I never have Wakka, Tidus, Rikku and Auron learn magic abilities. I've almost completed the entire sphere grid for some of my peeps and when I come accross some abilities for magic for the above 4, I just skip them. I'll take magic defense and stuff like that but no casting spells.
And for Yuna, Lulu and Khimari (yes my Khimari is a caster!), I don't let them learn any attack abilities including stuff like Zombie attack, dark attack, Mental break, etc, anything that has to do with hitting. These guys are pure casters.
I know I don't have to use those abilities if I don't want to but I'd rather have my peeps have tight identities and keep things simple. I wouldn't want to have to scroll down too much and avoid all the magic spells for example for Auron.