That in itself makes the Valuation an important historical record. But it also turns out that it can give a picture of the settlement patterns of Ireland over many centuries previous to the Valuation. The Irish seem to have done a surprisingly small amount of moving around their island over the centuries. The grown children of each generation tended to settle within a few miles of the rest of the family. Therefore in places where the Griffith Valuation shows a clustering of a surname, it often turns out that the historical accounts of the surname's origins will mention that same area. This can to hold true for some settlements/invasions going back nearly 1000 years.

A few examples are shown below in links to distribution studies on three Irish surnames in my own lineage.