In my classic D&D games, ability scores...
...can provide an XP bonus (or penalty).
...give a bonus (or penalty) to certain rolls. Strength modifiers melee “to hit” and damage. Dexterity modifier AC and ranged “to hit”. Wisdom I allow to modify all saves. Constitution modifiers hit points. Charisma modifiers reaction rolls.
...can be used for ad hoc “ability checks” to resolve actions.
Intelligence does the first for mages. You may notice intelligence is missing from the second. I never call for an intelligence check. So, if I drop the XP modifier for prime requisites, intelligence doesn’t really do anything and isn’t really needed. And I was never really attached to the XP modifiers.