Serfdom was widely spread in Germany from medieval times into the 19th century. The Duchies Oldenburg and Delmenhorst discontinued serfdom during their Danish administration around the 1700s. There exist records about manumissions (release from serfdom) and "Sterbefalls-Gelder" (fee to pay at a death). Such records reveal a wealth of information about family connections and their circumstances which would be of great importance to the family historian because this information supplements church records.
Source: Wolfgang Martens at www.familienkunde-oldenburg.de