Fatigue

[von Waldenburg]

In the storm you are slower. Another reason to remain still in a night storm, except if it's necesary to move for a good reason.

Diggin in or leaving it, changing travel/rail/patrolling mode, defensive firing or any other form of combat, all will add more fatigue during night turns. Actually the fatigue is added the turn after the actions are performed. So in a way you have to foresee it.

Moving an engineer to remove an obstacle will add fatigue to him but not moving into a mined hex to remove mines.

That's about it. The units that you want to rest should be in 2nd line at least or in inactive sectors. And the units that are in touch with the enemy should always return full fire at night and at day. Or otherwise not be at the front.