In this thread
http://forum.paradoxplaza.com/forum/showthread.php?t=235865
I was pointed to the fact that if in a province you have a road network and a extensive road network you don't have to pay for your troop upkeep.
The positive attrition modifiers for those 'building' are bigger then the maximum modifier for not paying for your troops, see also this screenshot.
In my opinion the attrition modifier for not paying should be much higher cause now you can fight a defensive war without paying for your troop upkeep.
http://forum.paradoxplaza.com/forum/showthread.php?t=235865
I was pointed to the fact that if in a province you have a road network and a extensive road network you don't have to pay for your troop upkeep.
The positive attrition modifiers for those 'building' are bigger then the maximum modifier for not paying for your troops, see also this screenshot.
In my opinion the attrition modifier for not paying should be much higher cause now you can fight a defensive war without paying for your troop upkeep.