Casting spells in passive mode.

[YUGON]

^This. Mages will never have their weapons out and will once again have a never ending supply of mana. Not a fan

They may manage MP another way. Like wait 5-10 seconds before MP starts to recover.
Anyway, this will help in not awakening a mob when you just cast sleep, because auto attack activates.

[Estellios]

I figured this would just take out the extra step of putting your weapon away if you're passive when you start the cast. If you aren't auto attacking or actively casting a lot you should be going to passive anyway to get MP back.