Why?
Well, its a further level of complication often with spells that have their own mechanics. And it sort of a mundane way of handling it. I guess there is no other way to handle rays. Personally I specialize in Area of effects that dont need it, and curse type spells that have save. I meant I dislike it as a mage and dont pick those spells generally, but I am not averse to the mechanic in the game.