The difference varies by location, in my experience.
For example - NYC had 2 enumerations of the 1870. For some of my family, they are all listed on the index page in 1 enumeration and singly on the other enumeration.
3 examples attached - the same family in 1870 in NYC - once with everyone showing, once with each individual separately. Also, a different family in 1870 in Georgia, listing everyone.