Roman writers rarely confused the Lares with the Penates, though both stood at the same household shrine and later readers sometimes blur them. The distinction was functional. The Lares guarded the place: the house itself, its threshold, its crossroads and the boundary of its land, and a family's Lares stayed with the house even when its occupants changed. The Penates guarded the store, the penus, the household's reserve of food, wine and oil kept in the innermost part of the house, and a family carried its own Penates with it when it moved, the way Aeneas is said to have carried the Penates of Troy to Italy.
Cicero and other writers pair the two so often that the household shrine is sometimes simply called the Lares' shrine even when Penates images stood on it too, which is exactly the conflation a careful reading corrects. The Penates could also be public, the great Penates of the Roman state kept first at Lavinium and later on the Velia in Rome, guardians of the state's own store and continuity, standing beside but never replacing the state's Vesta, whose flame was the public hearth the way the lararium was the private one.
The two cults reinforced rather than duplicated each other: a Roman household owed daily attention to both its place and its provisions, and kept a separate guardian for each.