The scrolls effects/damage scales with the respective stats in which the scrolls' branch of skills are tied to.
So, the magic paths: Aerotheurge, Geomancer, Witchcraft, Hydro, and Pyro are bound to INTELLIGENCE.
Man At Arms is bound to STREGNTH.
Expert Marksman and Scoundrel are both bound to DEXTERITY.
The higher your investment in each of the respective stats, the more effective a scroll becomes (in the same way the more effective a skill becomes).
To respond to the OP, yes it is great for scrolls to complement abilities other characters don't have, but also keep in mind scrolls don't have cooldowns, so if you ever need to cast the same spell more than twice (in particular healing spells), it helps to stock them up on the caster who normally uses the related spell anyway. Additionally, it's hardly effective to put a bunch of magic damage/healing related spells on a character who is running base intelligence stats- that character will more-than-often-not suffer a gigantic penalty in both action points and effectiveness.
Thanks, I myself learn new things every day
