I prefer spell charges in Final Fantasy I/III and Suikoden to a traditional MP system. In other RPGs, there’s usually no reason to use weaker spells once you’ve unlocked strong ones. Why waste MP using Fire 1 when Fire 2 will kill for sure? You’d only do it if you didn’t have enough magic to use a stronger one. Even if you wanted to save magic, you’d be better off just using a standard attack. But with charges, using a weaker spell doesn’t affect how many times you can use the stronger spell, because they have separate ammo pools. You also have to be very selective with when you use your strong spells, because you can only recover by leaving the dungeon and starting over. You have to think very carefully about whether it’s best to cast Fire 4 and watch as it slowly annihilates the powerful group of enemies in front of you one by one, or saving it by escaping or defeating them through other means.