Question: how exactly does Supporting Knowledge make spellcasting easier? What are the mechanics of this?
Suppose I have a +2 main skill and +1 supporting skill, and cast a spell that is fully included in both(example: healing spell with Restoration and Knowledge: Medicine). Do I get one action with a +3 bonus(quite reasonable, considering the sheer size of penalties this system has for most, if not all, worthwhile actions), or two actions with +2 and +1 bonuses(which would result in the chances of success dropping rather than rising as the amount of supporting schools increases)?
Just asking to be sure whether specialists are better off in this game than generalists.
Supporting knowledge tends to allow you to do different things, rather than granting bonuses or adding extra actions to things you already do. It works by making the principles, abilities, and knowledge of one skill available for use by another.
That example's kind of odd because there's so much overlap; it's more the kind of thing you'd see on somebody trying to be The Best Healer Ever than on your more typical character. Plus, medicine in the item/substance sense tends to be more for diseases, ailments, or slow recoveries, so knowledge of it probably wouldn't do a whole lot for most healing spells.
So overall, the main effect from supporting Restoration with Knowledge: Medicine would probably be that you'd be far better at magically easing joint pain and curing colds than a healer of similar Restoration skill. Supporting Knowledge:Medicine with Restoration would probably grant additional insight into the magically beneficial facets of certain medicines and components. If we're talking about Medicine as in all nonmagical healing, those effects would generally be similar, but broader and weaker.