Darth Canoli
Arcane
I remember some game (forgot which one tho) where you could permanently activate some buff-spells, but they would occupy a certain amount of your mana pool.
The buff would always be active, but 20 mana from your pool would always be locked as long as the spell is active, so if you have 100 mana you now have a maximum of 80 to use, and no amount of potions is going to push it above that.
Whatever it was, i played it too and it wasn't Titan's Quest or multiple games did it.
Dragon Warriors CYOA books did something similar with memorized spells, usually, it takes a full round to cast a spell, meaning everyone acts before you but you can memorize one or multiple spells which you'll be able to cast instantly but they reduce your intelligence by 1 (for each spell) so it's harder to hit.
If every buff you sustain reduced your chance of success of casting any spell in combat, it'd actually be a tactical decision to pre-buff, for you and the AI, except if the AI gets god-like characteristics.
I think this kind of dichotomy is only true if you're playing standardish all-rounder parties - 2 clerics/2 arcane casters /2 frontliners etc. If you however play unbalanced parties, this does not apply. You might be playing a noncaster party, that can't prebuff by the virtue of being noncaster. This party will still face opposition that will be prebuffing, so you're entering an asymmetric territory. Or maybe one char will be a caster, let's say a druid. The kind of prebuffing available to 1druid/5noncaster will be very different than what's available to 2 clerics/2 arcane/2 non casters. Or you might be soloing the game - no party. Or the gameworld is highly open and nonlinear and you will be going through it with a party of stealthy thieves using an offbeat metaknowledge path which will result in a very different distribution of precombat variables in terms of exp/weapons/consumables etc. than in your standard all-rounder party.
Point being, this kind of rationale of - if you don't need prebuffs don't put them in the game/if you need to prebuff all the time it's all braindead gameplay anyway so better not put it in the game as well - I think that's true only for median parties with median equipment using median path through the game. If you unbalance the game, it's all scrambled and you're no longer in this simplistic binary territory and having prebuffs gives you more options to unbalance it than if you didn't have them.
What are you doing man?
You're writing for the RPGCodex, don't try to over-intellectualize things.
By the end of your post, i had forgotten what we were talking about...