P.S. On page 12, it says you can declare the end of your Action Phase even if you still have fresh units. Although I don't know why you would ever do that.
It was added for completeness. If it wasn't there, I'm sure someone would be asking if they needed to activate all of their units.
I can also see it being used for victory conditions/scenario specific events.
For example, a scenario where one side it trying to load up supplies and escape might allow the defender to load one unit of supplies onto a truck with a squad that is still fresh during the Command phase.