The important thing in strategy is to suppress the enemy’s useful actions but allow his useless actions.
–A Book of Five Rings, Miyamoto Musashi
Flip it and you’ve got a game design maxim: make rules that block useless actions but do not block useful actions. Structure and rules can create order and set a baseline for good contributions but the danger is going too far and suppressing creative gold.
What happens if you do block the magic? Players will be annoyed. Or they will ignore your rules and do what they want. Often both.
Design craves to predict play but creative play is inherently unpredictable. It’s an uncomfortable situation.