Kingdom Hearts II Abilities' MP Cost

It's probably for the explicit purpose of making their MP gauge recharge after the use of another ability(unless items are used). It's probably to make them marginally more useful because allies in KH generally aren't good for anything aside from being pack mules for potions and ethers.

 

If I had to guess, I'd say it's a replacement for turning off MP charge for magic abilities. I do that all the time so I can use attack magic (basically) all I want, but then still have at least 1 MP left over to cure.

Giving you the option to disable MP charge for your allies' moves would complicate things too much, and if you're really on top of your healing, then after a while the ally would be stuck with low MP and wouldn't be able to do any powerful attacks that require MP. They would have to heal before their MP would start recharging again.

So basically it lets your allies be a little more useful. They can heal, and then still have enough MP to use another one of their techniques (or just heal again) before having to recharge. It would be boring if they were just your healing slaves (though you can still set their behavior to do that if you want).

 

Not entirely sure. Maybe since he's always with you by default, it would be too good. Like, you could exploit it more easily with tough/secret bosses, by setting his behavior so he only heals you, so you get two heals out of him per recharge. I guess it also kind of incentivizes you to use the world-specific party members by making them a little better. It's a trade off for not being able to use that ally's drive form.

If you insist :P