A link (or at least a page reference), from the bibliography to the citing command, is often useful in large documents.
Citeref is the older, and seems to rely on rather simpler (and therefore possibly more stable) code; it produces a list of page references, only. It doesn't interact well with other citation packages (for example, cite), which probably reflects its antiquity (it's derived from a LaTeX 2.09 package).
Neither collapses lists of pages (“5, 6, 7” comes out as such, rather than as “5–7”), but neither package repeats the reference to a page that holds multiple citations. (The failure to collapse lists is of course forgiveable in the case of the hyperref-related backref, since the concept of multiple hyperlinks from the same anchor is less than appealing.)