The way I kind of see lieutenants is analogous to a professor and his
grad students. A regent can tell his lieutenant to go and
do something special, but he'll probably have to invest
some of his own time when the lieutenant inevitable gets
stuck. Thus the 1 extra action.

Vassals on the other hand, may be more like the relationship
between the head of a faculty and the other professors. Sure
he has some influence, but he doesn't have complete control
over their actions.


P.S. The way that I see the faculty head - prof - student
relationship is just what I've picked up over my
many years as a student and may be totally off