Not sure if this has been covered before but it seems that the old strategy of boosting a province's economy by disbanding peasants/militia/any unit in it no longer seems to work as it did in RTW.
I disbanded 6 units of peasants in Durazzo to bring it up to next castle upgradeability only to find next turn the populace had only increased by the statutory 2.5%. The population figure definitely didn't increase every disbandment a la RTW.