The reason for the "where-used" is because we have retired several phrases over the years and want to give our customers the ability to clean up their phrase library. The retired phrases could either be phrases that were used as input to rules, or were outputs of rules. One should do a "where-used" first before deleting, as the phrases may still be present in specifications. The alternative would be to re-run the "rules" on all products so that the old phrases are removed from specifications and replaced with the new ones, but that's an unreasonable approach.
With the limited functionality of the "where-used" feature, I think we may be stuck with having these phrases remain.
Thanks for the HANA info, i will check that out, it sounds promising.