As anyone will tell you, the three most important factors in real estate are location, location and location. No doubt, any genealogist will likely tell you the same.
What this means is you can not go very far in any family history without location becoming a crucial element in you research. Location features in every census, birth or death record. Newspapers may report on national and regional events, but the ones genealogists care about tend to focus on more narrow locations: a city or sometimes even a neighborhood, which will include the details of residents that might hold a sliver of the story of our ancestors lives.
It should be no surprise that professional genealogists tend to narrow their focus based often on location. There are very few true generalists in pro circles because it’s hard to keep track of the changes in boundaries in any given area. Throughout history, city, county, state, and yes, even country lines have changed due to political and military forces. With all of those changes, primary repositories responsible for records of the people of the region have also changed.
Additionally, different events in a person’s life are recorded at different levels of church and state. In modern times, a birth will probably be recorded in the city or county, yet in the US, the federal government will also have a record due to issuance of a Social Security Number. The church parish, if one participates in such an organization, will have record of a baptism and not the actual date of birth. Contrast this with 200 years ago, when civil registration of a birth was not legally required in all places. The baptism was often the only record the parents thought was important or required.
If a birth was recorded with the civil authorities, it may be listed in the town or county records, but the area that encompassed the town may have split into two or three other towns a decade or two later. Or the county may have split into two counties 50 years later as the population increased. A record search will only be successful if focused on the repository of the county when the record was created. To complicate things further, the records should be in the original repository as expected, or they might have been transferred to the new clerk, or sent to a larger state archive at any point between then and now.
All of these issues are amplified when dealing with state and country line changes. It quickly becomes obvious how helpful it is to have a professional genealogist who has a deep understanding of the factors influencing records in the region your ancestors lived. Otherwise, you may very well be shooting in the dark.