Isn't using scrolls the only way to increase spellcasting skill? Wouldn't it be better to amass twice if not thrice as much scrolls than to use large amount just to increase skills?
Yes, and it depends on the scroll. Summon scrolls are useful for training, as there are little strategic use to them, but you'll want to keep the ones that boost unit stats or hurt enemies. Summon Scrolls are also more common. Higher spellcasting skill makes it far more likely for the scroll to succeed, so casting off a few summon scrolls to up your skill while you're in a safe position so you can get off that Scroll of Pain and Suffering when you need to is a good trade-off.
