I didn't really like Materia, simply because you'd be absolutely helpless magic wise once it's removed from a character.

At least with systems like FFVI's you would still have the magic and stat bonuses that you gain from the espers even if you de-equipped them. With FFVII's if you de-equip them your character won't have the magic/skill anymore. It's kind of strange levelling up a lot of Materia on one character only to have them not have the magic/skills anymore one you remove them.