Just a thought, not recommending it, not like it’d happen anyway… This thought draws from my experience playing a few games from the Ultima series. If your magic ability wasn’t trained well enough for the circle of magic you were trying to cast from, the incantation would sometimes fail, and you’d still spend the mana for that spell cast, and in some games the reagents.
To make the Energy stat more useful;
All classes have a base % chance for magic abilities to fail casting, and the failed cast consumes half of the mana. The higher the energy (intelligence) stat is, not only would you get more mana, but it would also reduce the chance of a failed cast.