If true, bibliography entries which are not cited are suppressed. A biblioentry is cited if an XREF or LINK matches its ID, or if a CITE element matches its ID, XREFLABEL, or leading ABBREV.
A BIBLIOGRAPHY with no entries will still be output (making a whole component conditional would be _A LOT_ of work and seems unnecessary), but BIBLIDIVs with no entries will be suppressed.
This setting may have significant performance implications, hence it is false by default.
(This option can conveniently be set with -V biblio-filter-used on the Jade command line).