There are any number of movies where a key scene involves someone “getting across the county line” so they will not be arrested. While genealogists are not usually worried about being arrested or directing movies, the fact that things change when you cross the line is one to remember.
Crossing any political line, including whether it be one of county, state, province, territory, or nation, may mean that the laws and recordkeeping system may change. In some cases, the change can be significant. Even when crossing states/provincial lines, the laws regarding what is recorded and how it is recorded may change. Learn about the new area’s records before you assume that Virginia in 1760 is just like Nebraska in 1860. That’s something of an extreme example, but it hopefully makes the point.