Yeah it's fairly common and nothing fancy.

I would like to point out, that the formation DOES NOT work as well if the three rear units do not have guard mode on.

With guard mode, the entire unit does not engage in combat as soon as neighboring units do, or lead units do, which enables them to fight at full strength for much, much longer.

Have you noticed that a unit on attack mode will tire quickly even if it doesnt see combat, merely because it is adjacent to a unit that is attacking? As long as the big giant blob spreads out in engaged mode, every man tires at the same rate, in combat or not.

Any non-attacking units should be on guard mode. I seldom use it unless I'm in a seige defense situation. However, on walls it is a bad thing because the objective is to surround and crowd the enemy to death before they can get situated. On walls is a must-attack situation.

This advice is meant for newbie players, as our veteran members probably know this already.

As to your other point, yeah town militia doesnt fare well against high attack armoured units with good stamina and morale. However, the way I play, it's never come up. By the time the AI or rival factions have such units, my territory has expanded to an obscene size, and the only armies I have are offensive in nature.

Sometimes the best defense is a good offense.