The Weighted Flank group of tactics is the anti-thesis of the standard formations of old, exchanging the traditional symmetry and central infantry lines for a localized concentration of force on one flank. In my experience the weighted flank is THE way to defeat horde armies. Especially if you have a faster force that is hth driven.
The Weighted Flank formations involve heavily beefing up one flank (the Strong Flank) with the bulk/cream of one's troops in order to create overwhelming local superiority and achieve a collapse of that flank. The other flank, known as the Refused Flank, may be left totally empty or, as is more advisable, held by light troops whose objective is to slow the enemy down and prevent them from assisting their comrades. It is considered a Weak Flank if the line stretches into it, but the units in this part of the line would be considerably weaker than those on the Strong Flank.
The Classical Weighted Flank.
An asymmetrical array of units with the preponderance of strong units on one wing.
On occasion, formations weighing both flanks ("Empty Centre") may be seen. When used defensively, it becomes a hedgehog or fortress formation, which will be covered shortly.
It is most useful against horde armies, or those who are similarly spread out and vulnerable to a focused application of pressure. By concentrating our forces on one flank, we are creating a situation where that flank becomes isolated from the rest of the enemy army, which has to spend a few turns coming to their aid, and is beaten piecemeal. In theory, we are trying to hit half the enemy army with our whole army (sans the units holding up his other half), overrun them, and then turn around to meet the other half, again with our full army. Most of the time, however, if the opponent has deployed well and kept his units united, then he can wheel his army to meet ours fairly comfortably. It is the horde armies whose lines stretch from one end of the table to the other that will have problems reacting to the Weighted Flank attack. Speed is also a large factor with this tactic. The more of a speed advantage you have, the more you can trick your opponent to spread there line across the board. With speed you can quickly refuse a flank and add more concentrated power to one flank. A force like Eldar can literally deploy flush across the board and redeploy in one turn.
Locally, we take turns to deploy one unit each until the entire army is deployed. So having fewer units is a big disadvantage as you have to reveal your main force before the opponent places his. This formation helps mitigate this somewhat by keeping our army together not spread out and vulnerable to the enemy's own concentrations of force. The caveat here is that the enemy does not have overwhelming superiority in ranged attacks, in which case it can quickly turn into a disaster.
Refused Flank formations are also useful tools against guerilla armies, as it denies them the chance to prey on stragglers. Keeping together, it is harder for the enemy units to gather enough force to stop a full out charge, as there tends to be to many units to deal with at once.
A Weighted Flank formation is also one way to tackle a Breakthrough scenario, creating a localized break in the enemy line to shepherd the units through for the touchdown. However, this runs the risk of being totally held up if the lead units run into tarpits.
Empty Centre. Lure the enemy down the weak centre, then crush him in the vise formed by the two strong flanks.
Frontal Assault. A direct attack by the Weighted Flank, while the Refused Flank carries out a holding action.
As mentioned above, if the enemy has ranged superiority and digs in on the other flank (ie. opposite our refused flank), then we have just dramatically increased the distance our troops have to march under fire to reach him, which can only mean higher casualties and poorer prospects for victory. If the opponent has deployed his units well, the Weighted Flank formation may not confer much of an advantage. Worse, if the opponent has the first move and is able to advance aggressively, or if our own assault breaks down, we might find our entire army hemmed in and under attack from two directions.
Catastrophe. The enemy castles into the opposite flank. Blue army faces a long march to the enemy lines.
Counter-assault! The opponent meets the Weighted Flank attack with aggressive advance of his own.
Besides the frontal assault, an army with speedy units may attempt the Sweep Left/Right, especially if the enemy has guessed our deployment and our Weighted Flank faces a morass of infantry units that doesn't look like they can be broken through easily. If pulled off successfully, we would have diverted our attack onto the other flank, while the enemy units which were placed to hold our Weighted Flank struggle to catch up. However, do not make the mistake of attempting the Sweep when the ipsilateral flank (the flank directly opposite) contains enemy fast units, as they can catch you with a CounterSweep.
Sweep Left. Catching the enemy by surprise with a diagonal attack on the other flank instead.
Counter-Sweep. The Sweep is fraught with danger. Blue makes an inappropriate Sweep and is caught out.
Alongside the Balanced Line, this is one of my most used formations. It may not be as flexible, but offers fairly safe deployment and a chance of quick and painless victory against careless opponents. Although it should be noted that I tend to play small elite armies, not hordes.