Apparently he carries codes to change the alliances of the storm troopers (in addition to the plans of the death star, I suppose), who in III turned on the Jedi.<p>This theme is/was meant to come in part VII-IX.<p>I read this on Slashdot.<p>At the end of VI the death star is destroyed, but whoever can take control of the storm troopers on the remaining imperial starships is a force to be reckoned with.