Materio
"Whatever..."
Cover Materia was awesome, it allowed you to choose who to build their Limit Break levels first, if you wanted. Also, using it saves a lot of MP. For example -
Without Cover, all three characters are attacked frequently, so, once you've used Cure-All (if you have it), you have to use up MP to cast 3 x Cure.
With Cover, one character takes the majority of damage. Only one Cure spell necessary, as only one character takes noticeable damage.
So...
Cover - Saves MP and allows you to concentrate Limit Break levelling on a specific character of your choice.
Without Cover, all three characters are attacked frequently, so, once you've used Cure-All (if you have it), you have to use up MP to cast 3 x Cure.
With Cover, one character takes the majority of damage. Only one Cure spell necessary, as only one character takes noticeable damage.
So...
Cover - Saves MP and allows you to concentrate Limit Break levelling on a specific character of your choice.