Thanks all.
What about the idea of a "Suppressed Magic" zone? To cast a spell the PC would beed to pass a DC check.
I'm not actively thinking about putting any of these in a campaign, but I was thinking about their inclusion and I'm having a hard time seeing the benefit beyond novelty.
Story/world reasons.
In Pathfinder's Golarion you have, I believe, the Mana Wastes a wild magic and dead magic region between two historically warring super high powered magocracies who hurled magical catastrophes at each other. This can be seen as having disrupted the stability of magic in the ground zero area and took out some enemy magic resources and leaves design space for a non magical culture to flourish there after the magocracies abandon that front (gunslinger land develops from magocracy war refugee community in magic dead zone).
Similarly in
Kobold's Midgard Campaign Setting you have
the Wasted West an area that had been devastated by an archmage war where Cthuloid entities were summoned as WMDs and the solution when you can't banish them was to partially time stop despite their reality radioactivity area of effect even when mostly frozen in time. So now the land there is filled with mutant goblins and wild and dead magic zones would not be out of place.
As a practical matter for adventuring, if they are part of the world it should be for a different novel adventuring experience. So the party can prepare before going in, or get thrown there unexpectedly and have to deal with it. Similar to plots of being captured, or going into a purely social setting without magic and armor and weapons, or going underwater where some standard things don't work , it can be a neat change of pace, a neat challenge, or frustrating and fun killing, depending on specifics.