Summaries of census records on subscription services such as Ancestry.com provide helpful information. However, the summary does not exhibit all the data captured by the census enumerator. Take a look at the actual record.
Example: The census summary does not show the amount of personal property owned. For southern records before the Civil War this item can be revealing. A southern farmer with a large amount shown as personal property in 1860 may have been, and probably was, a slave owner. While slave schedules also exist, they are spotty and not always reliable.
As many slaves took the surname of their owners, this could be helpful for African-Americans researching their roots.