The advantages of modeling how a target language syntax tree moves with respect to a source language syntax tree are that (i) we can capture the fact that constituents move as a whole and generally respect the phrasal cohesion constraints (Fox, 2002), and (ii) we can model broad syntactic reordering phenomena, such as subject-verb-object constructions translating into subject-object-verb ones, as is generally the case for English and Japanese.
there is also significant amount of information in the surface strings of the source and target and their alignment.