Given the relatively high cost of Settlers, this Policy is very useful to cut down production time during your initial expansion period. As with other specific production-boosters, it would be nice to churn up several Settlers one after another; however remember that there is the small detail of the File:Citizen6.png Population of the source city diminishing by 1 for every Settler produced (or Purchased)! So, maybe you should adopt Colonization only from time to time and produce one unit at a time, so as not to cripple your source city too much.