With the Grimoire mini game that is tied to the Wizard tower, there are several spells that can be cast. Each of these spells have a cost that use your magic. This cost is a % of your maximum magic plus a flat rate.
According to the Cookie Clicker wiki, there are optimal max magic amounts for the shortest time to being able to cast the spell again.
How do I interpret this though? Does getting higher magic max make it take longer? Does higher magic max just give diminishing returns? Does a magic max that is optimal have a large difference compared to having a gross overkill amount, like having 700+ wizard towers compared to the usually low (like 70 maybe) that the optimal amount needs?