For hand-written deep parsers, efficiency and coverage are often competing factors: allowing more items to be created might be beneficial for recall, but the parser will also be too slow.
the authors show that a large, hand-written, unification-based parser (the XLE LFG parser for English) can perform reasonably faster (18%) without losing accuracy, by not allowing the parser to unify if the resulting item will have a span that does not conform to a CFG tree that was generated from the sentence beforehand by a PCFG parser.