I feel like magic has been missing one thing, I was surprised initially when I learned of this. My issue is that magic has no persistence. Like I'd cast earthquake and then a healing spell and the latter would overwrite the former.
I can't think of any reasons why we would not want to be able to cast more than one spell at a time, it would greatly add to the usage of spells and diversify combat for magic users. Sure make it so you can't cast 2 earthquakes, but please let us combine spells
*Spells with a duration do not have that duration ended upon casting another spell. Reworded slightly, figured it might help anyone who views this. I have to hear things 2 or 3 different ways sometimes.