1790, 1820-1840 have very little data. However, that data is useful in discerning how many children are from one census to the next, if they were married or died, etc. It is always useful. Example: One may examine these records and compare the tombstone of a child found in a cemetery that may belong to their family.
Also, to identify later surnames which appeared in the records, such as persons listed on militia records and in revolutionary war applications etc.
Genealogy Tips