
I mean: mage or priest couldn`t cast any spell on this area. Monsters, of course, could cast their spells there.
For example: before You enter that special area (or level) You have to prepare a lot of potions, or devensive spells (like party shields), for Your party, because inside "non-magical areas" You would not do it.
What do You think about this? It would be usefull when making a custom game. For a player, explorating that area would be harder, than normal ("magical") area.