1. By being able to maintain spells (shield, blur...) a caster is free to attack or maneuver during the first rounds of combat, when he'd otherwise have to be casting spells. Also the effects of these spells are around on round 1 of combat.
As I say, I think nobody maintain these spells since morning as prevention for instant combat, you need to use 5 PPs (2 + 3) every 10-15 min., then at mid-day (6 hours) you waste about more than 100 PPs...PPs must be saved at any cost as you can!.
2. Spells are no longer limited by their duration, they're limited by the PP's of the caster. The caster who can fly further without having to land to recast the spell was my previous example.
Yes, that is the vision, duration is how often it takes energy...for short duration spells. But for spells like preservation and others duration is very important, as you need to be in range to renew it. So IMO this is not a big change.
3. And finally, 1 specific example, Haste. Imagine a level 6 PC hasted for 10 rounds, a level 12 for 30 rounds, or a level 15 for 50 rounds.... a level 20 character could likely maintain Haste X for at least 100 rounds, that's over 15 minutes.
Haste has no duration, the reason, it is not allowed to increase its duration with spell mastery or spells in list 'spell enhance', as it is required the spell as duration.
Out of combat... for the most part, this isn't a big deal (aside from flying or invisibility examples), but in combat your giving the caster double activity on the rounds he 'maintains' spells rather then having to recast them. That a major unbalancing issue. It's not just giving the casters an additional 10% (for instant spells) or 90% (for normal spells) activity... it's letting the casters cast an ADDITIONAL spell during that round. So far as I know (someone please correct me if I'm wrong) there is no way, what-so-ever, that a caster can cast more then 1 spell in a round; ergo, allowing casters to, is a fundamental balancing change. On top of that, they don't need to roll a SCSM to 'maintain' the spell.
Most combat/defense spells are instant, and you don't need to add an extra casting spell, unless all your spells are type-I (no preparation) you can cast the instant defensive/combat spells while preparing another one (90% preparation + 10% cast instant), you don't need to cast these spells at the exact momment it go off, near the end you cast them while preparing your 'lightning bolt', for example.
In any case, in our game that is not important and/or unbalance, as we allow to cast 2 spells per round with some requisites:
1) Only 1 spell can be offensive.
2) You need enough activity, of course. But if you haste you could cast 2 spells type-I (75% + 75% activity) with no problem while only 1 is offensive.
This allows interesting combination, like 'jump + fly', 'turn spell + attack spell' (so 'spell reins' list is really usefull for magical combat). We are not very agree about that automatic limit of 1 spell per round "yes-or-yes". After try, we use this rule that is balanced and it has not problems like casting many 'words' in 1 round, as only 1 offensive spell is allowed. But we want that defensive/utility spells was really usefull.
Has anyone (apart of us) the sensation that those spells are like in second plane many times?.
One example, magical combat, magician vs magician, first has 'spell reins', but second always attacks it with a type-I spell 'bolt', so it can cast any every round, adding that 2nd has much more initiative (QU), in this case magic combat is determined by initiative, and not by spells known, if I spend DPs learning defensive spells, why must be initiative more important?.
Adding that defensive spells usually takes more PPs than attack ones, the 1st magician spend its PPs earlier, the combat is finished, initiative is the winner.
With our rule, 1st could use 'turn spell', as it is instant, it could prepare and/or cast its attacks spells at the same time, there must be some advantage in spending DPs for adquiring 'spell reins' instead 'invisibility ways' in this case.
Second example, 'spell enhance' list, 'increase range' spell, we have normal and instant version, 2nd has greater lvl of course, but what is the utility of that?, you need 2 rounds in any case to cast the increased range spell. So imagine this case: you are passing a precipice using a thin bridge, using balance, passing 1 by 1, anyone can fail so a player (other than spell caster) falls off, in this situation you can't wait 2 rounds, so your only option is cast 'increase range instant + some teleport spell', as teleport spells usually has only a range of 10'. I don't see the problem at all of making these spells really usefull.
If all of your party/world are casters, no big deal, but as Markc pointed out earlier, if your going to do something like this, the arms professions need a way to keep up as well, perhaps let them attack twice every couple of rounds?
We use an improved 'combat styles' method that gives much versatility to arms, as they can be boring for players only increasing the OBs. If you are interested I can mention it here (I think I did it in another post by I am not sure).
