[thejeff]

20 is higher than I'd usually go. But even 10 or 15 can force your enemy to invest more in his raiders and thus have less available. That'll usually stop things like Arouse Hunger or Call of the Winds and even cheaper thugs.

While you could do the same by recruiting troops and stationing them everywhere, at those levels PD is often as good as the same gold cost in troops and doesn't use upkeep. Sure, you could buy more Forts/labs/temples or more mages, but the potential loss of all the income and gem producing provinces on the first turn of a war is devastating.