On the help page sentries are supposed to fight better in their own regions, move slower, and suffer morale drops when out of their regions. What exactly is this "better fighting"? I have definitely seen slower movement, but I have also not seen any significant drops in morale even when I once moved sentries hundreds of miles away from home.
What about mercenaries? I know they need more gold, and they supposedly deal better with being moved far from home. What about combat effectiveness?