Particularly, Liu and Huang (2014) show that by requiring the conventional parameter tuning algorithms to consider the final decoding results (full translations) as well as the intermediate decoding states (partial translations) at the same time, the inexact decoding can be significantly improved so that correct intermediate partial translations are more likely to survive the beam.
the underlying phrase-based decoding model suffers from limited distortion, and thus, may not be flexible enough for translating language pairs that are syntactically different, which require long distance reordering.