While a pedigree chart reflects the line of ascent or descent in the family hierarchy, a family group sheet presents a picture of the structure of a family unit and gives details about the family members. It is important to examine that structure carefully because the birth order of the children can be very revealing. A child's place in the family hierarchy is important for a variety of reasons, not the least of which are the records left behind to assist your research. Some researchers concentrate their investigative efforts on nailing down vital dates for only direct ancestors. But ignoring your ancestors' brothers and sisters can be a costly omission.
Birth order is important.
Family structures have changed over the centuries. Couples typically produced more children in earlier times than they do today. Above and beyond the joys of a large family, there were practical matters to consider. They also married, producing alliances with other families and perhaps bringing additional resources into the family. And of course, they produced additional families of their own.