Basically turn based action points will fixes most of potion spam problem. In older game you have to juggle with do I cast a spell now and possibly end the fight or try to heal so I don't lose a party member. Even if you have unlimited amount of potion(say a meditation skill that cost only action point to regen mana), you are still bond to the turn based nature of game flow, you can't get instantly 3 mana potions that stacks and fill your mana while you can still continuous magic, it just won't happen.
Mana/Health recovery is always a big part of RPG game, if shows the progression of your character, you can cast more spell, become stronger and take more hits, so as the amount that you can recover from lost/used ones. And turn based happens to be a really easy way out to avoid exploits and spam.
You always facing possible critical roll, in tough fight that's what keeps everyone on their toes.
