Decreases the mana lost per point of damage taken when Mana Shield is active by X% and increases the resistances granted by Mage Armor by Y%.
Arcane Shielding is a mage talent that decreases the mana lost per point of damage taken by your Mana Shield spell, and the resistance gained by Mage Armor. Mana Shield normally costs 2 mana per point of damage absorbed. At rank 2 of this talent, Mana Shield will only consume 1.6 mana per point of damage. This talent does not have any affect on the initial casting cost of Mana Shield, only the mana used by the shield itself.
Mages who use Mana Shield often, such as in PvP, might consider taking this talent. Mana Shield is one of the primary defensive spells, especially for non-Frost mages. Mana Shield (Rank 7) will use 1585 mana without this talent, and only 1299 with 2 points talented, for a savings of 286 mana. It is still expensive, but the savings might be worth it for some mages. Deep Arcane specialized mages usually have more mana.