[FT] Operational game

One of the problems with an operational game is how you divide your
forces.  Let's say both fleets start at 5000 points.  Ideally, an
admiral is going to want to have all 5000 points show up on the table,
but this means that each operation has exactly one huge battle.

Okay, we give each side several points to defend.  So one side gathers
his forces and hammers the other side's detachments, which either have
to flee or die--not an interesting battle either way.  We want to have
several, reasonably even matches.

So what would induce an admiral to hold back some forces?  Fear of an
ambush is one; having a limited control span is another.  What else?