This policy provides you and your allies with extra Food and Production if you send Trade Routes to their cities, and also speeds up the rate at which both of you earn Alliance Points. It's extremely valuable when playing as Poundmaker.
Civilopedia entry Edit
As Dutch cities became centers of banking during the early modern era, so too evolved the need to handle bills of exchange among merchants in a stable, trustworthy way. The Wisselbank acted as a sort of commercial lender and broker, offering its own bills to facilitate transactions between traders, with its own reserve of valuable metals. The bankgeld notes are some of the earliest examples of fiat currency in Europe.