It's what is called an art continuity sheet.  For 
the most part, it fills the same role as the 
Storyboard does in American style animation.

From what I've seen, the original ones very 
rarely make it out of the studio, or the original 
artists posesion.  But during production there 
will be several copies made for the genga artists 
and other animators.  It's not uncommon to find 
little notes, doodles or other drawings on these 
which can make them fun to look through.