This module provides a new widget for a term reference field that displays the parents of a term matching the autocomplete as well as providing actual TIDs back to the form handlers.
This differs from a standard term reference autocomplete that presents a flat list and only returns the term's name value and tries to suss out the TID from that (which is not guaranteed to be the right one in a hierarchical vocabulary that might have replicated terms). A use case might be:
Honda is a valid model for Bikes and Cars, but you don't necessarily want to lump anything made by Honda all together (think classified ads, reviews, etc).
While Wim's Hierarchical Select widgets are great, we had a need for a multivalue autocomplete that presented the hierarchy in a dropdown.
There are no plans to backport this to D6.
My employer Phase2 Technology graciously supported my turning this internally developed module into a contrib module.