mmh... but why not? staling tactics, waiting for 1) your reinforcements to come from the rear lines keeping the enemies at bay or 2) your rear lines to organize better the rearmost defences, are the bread and butter of the military campaigns.
Have you ever played Call of Duty, seen Saving Private Ryan (last battle), seen the movie 300?
If you did you know what I'm talking about
Sometimes battles last more than one month because the defenders of one territory, even if doomed to lose on the long time, just doesn't want the enemy to pass through a point immediately and come out with tactics to slow him. Even in real world, without fatiguing magic
So why to change this well-implemented feature in the game?