Yeah, I don't think the problem is so much the ability to cast buffs technically before battle starts (as opposed to just before the fighting actually "begins," but after the start of battle), as much as it is with the whole premise of stackable buffs, in the first place. But, especially when you can just casually cast 10 things outside of combat on, say, your Fighter, you have to look at it from a capability standpoint. How much of an advantage does it give you to do that? If it's a huge one, then it's something there's pretty much never a reason not to do that's making all combat encounters that much easier. "I just negated all the effects of the enemy's combat group makeup BEFORE WE EVEN CLASHED! HAHAHA!" What's the point in having such varied enemies to have to cope with if you provide an easy way to simply never have to deal directly with those enemies' unique combat factors?
If it's not a huge advantage, then either those spells are kinda pointless (if you have to stack 10 just to get a "meh" advantage), OR, combat is balanced against your stacking those spells like that, meaning it's essentially "necessary" (not every single fight, but, in general, the game bets on you doing that, and if you don't practice pre-buffing, you're pretty much not going to make it through the game). In which case, aren't there more fun ways of designing that in the first place, than requiring the group to just pre-buff up before going into combat, just to gain a fighting chance?
So, I dunno... it's kinda hard to limit spells cast before combat
without simply denying the ability to cast any of them at all. If you have spells that can be cast at any time, and they last X amount of time, then you can stack them all, THEN enter combat. You either have to make them all really short-duration (which hurts in-combat
functionality and design), or only let them be cast within combat (so that your casting decisions are tactical and meaningful, rather than just freebies).
I very much think that Mr. Magniloquent's idea is a good one; quantity limiters. However, it still seems like the quantity of spells on a given character should be more limited outside of combat than it is inside combat. If you can manage to get 3 spell effects on someone WHILST being attacked by a whole group of enemies, that's one thing. But, if you can still just do it for free outside of combat, then, well, you've got the benefit of a quantity limit at least (so you can't just stack 18 spells, then charge into combat), but, it still seems like there's a better way to do it than just allow spell-stacking before combat.
I mean, same thing with traps, sort of. Sure, you can lay traps before combat, but, just putting a cluster of 17 bear traps, then luring the enemy group into that one blob and killing them all is a bit silly, really. It's kind of anti-tactics. The combat encounters are supposed to be easi-er
if you do it right, not just-plain effortless. Also, you'd think a cluster of bear traps would be much easier to spot than just individual ones. Kind of like how a group of people is easier to spot sneaking around than just one sneaky person. So, maybe have traps lose like -1 from their Spot-ability DC if they're too close to each-other? Something like that...
Anywho, I think there's plenty of room for pre-combat preparation without specifically casting duration-based beneficial spells on characters before entering combat. There are a lot of ways to do it. You could even do things like allow each person to have 1 prepared spell/ability (supportive/augmentative) that auto-activates at the beginning of combat (basically when your party goes "All right, let's DO this!" if they've got the jump on stuff, or "Oh crap, BATTLESTATIONS!" if you didn't know about it beforehand), whether on that character's self or another friendly target, depending on the ability. Or, maybe you couldn't use these if YOU didn't initiate combat or something, *shrug*. Or, maybe it's as simple as "once you successfully cast the first 'round' of spells, the enemy gets to act," so you just control it manually just like pre-buffing, but you don't have to jump out waving your hands and yelling before you get to cast buffs and stuff.
*shrug*, I just really don't think casual effect-stacking is a good thing to need in the game, in any capacity, as there are much more engaging ways in which to allow for preparation and meaningful buffing. Spell-stacking just turns level-up/progression power partially into stacked spells. "You're more capable because you have more effects to stack on yourself before combat even starts." At the very least, if that's the intent, then you might as well just let them all auto-activate instantly at the beginning of combat, even if they were to still take up Vancian "ammo" each time until you rested.
That being said, I'm also very much in favor of a lot of utility
spells being castable and useful outside of combat. Like Light (to visually lure enemies), etc., as Nonek and others had mentioned up near the top. But, for the most part, I think combat is best served by borrowing Vegas's slogan: "What happens in combat, STAYS in combat."
. For the most part...